Assessing quality of volunteer crowdsourcing contributions: lessons from the Cropland Capture game

Volunteered geographic information (VGI) is the assembly of spatial information based on public input. While VGI has proliferated in recent years, assessing the quality of volunteer-contributed data has proven challenging, leading some to question the efficiency of such programs. In this paper, we compare several quality metrics for individual volunteers’ contributions. The data were the product of the ‘Cropland Capture’ game, in which several thousand volunteers assessed 165,000 images for the presence of cropland over the course of 6 months. We compared agreement between volunteer ratings and an image's majority classification with volunteer self-agreement on repeated images and expert evaluations. We also examined the impact of experience and learning on performance. Volunteer self-agreement was nearly always higher than agreement with majority classifications, and much greater than agreement with expert validations although these metrics were all positively correlated. Volunteer quality showed a broad trend toward improvement with experience, but the highest accuracies were achieved by a handful of moderately active contributors, not the most active volunteers. Our results emphasize the importance of a universal set of expert-validated tasks as a gold standard for evaluating VGI quality.     

Landscape variations in stream water SO4 and δSSO4 in a boreal stream network

Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO₄²⁻ and δ³⁴S_SO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S-SO₄²⁻ concentrations in stream water averaged 1.7 mg L⁻¹ whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L⁻¹. A significant negative relationship was observed between S-SO₄²⁻ and percentage wetland coverage (r² = 0.77, p < 0.001) and the annual export of stream water SO₄²⁻ and wetland coverage (r² = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO₄²⁻ concentrations and the annual export of stream water SO₄²⁻ (r² = 0.77 and r² = 0.79, respectively). The annual average δ³⁴S_SO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ³⁴S_SO4 values decreased in all streams by 1‰ to 5‰. The δ³⁴S_SO4 values in all streams were higher than the δ³⁴S_SO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha⁻¹ yr⁻¹ (wetland headwater stream) to 3.8 kg S ha⁻¹ yr⁻¹ (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha⁻¹ yr⁻¹ (2002-2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.     

Numerical simulation of the plasma double layer

A one-dimensional particle-in-cell computer simulation is used to model the formation of an electrostatic double layer. The conditions for the onset of the layer formation are explored and a relation between the length of the layer and the electrostatic potential difference across is found.     

Flood frequencies reveal Holocene rapid climate changes (Lower Moulouya River,northeastern Morocco)

Current high‐resolution palaeoenvironmental records reveal short‐term Holocene coolings. One of these major Holocene rapid climate changes occurred between 3.2 and 2.7 cal. ka BP. The sensitivity of river systems vis‐à‐vis slight and short‐term Holocene climatic variations is a subject of controversy in the scientific community. In this paper, we present a 4.0 to 1.4 cal ka BP palaeoflood record from the Lower Moulouya River (northeastern Morocco) to demonstrate the high sensitivity of semiarid rivers in the southwestern Mediterranean towards Holocene environmental changes. The Lower Moulouya flood deposits are characterised by thick, well‐stratified, predominantly clayey to silty overbank fine sediments. These cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late Holocene flood sequences. The Moulouya palaeoflood record can be interpreted in the context of regional and global high‐resolution proxy data, revealing a strong coupling with Holocene rapid climate changes. The centennial‐scale Moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record (palaeomagnetics, sedimentary charcoal record, anthracological analyses, snail analyses) to generate new ideas about the mid to late Holocene hydrological cycle in the southwestern Mediterranean. The deduced features of pronounced Lower Moulouya flooding and the decreased fire recurrence during Holocene cooling remain somewhat inconsistent with the interpretation of other palaeohydrological and paleaoecological records from the southwestern Mediterranean. However, enhanced Lower Moulouya flood frequencies between 3.2 and 2.7 cal. ka BP agree with increased floodplain aggradation in other major river systems of Mediterranean North Africa. Copyright © 2009 John Wiley & Sons, Ltd.     

IFKIS-Hydro: an early warning and information system for floods and debris flows

IFKIS-Hydro is an information and warning system for hydrological hazards in small- and medium-scale catchments. The system collects data such as weather forecasts, precipitation measurements, water level gauges, discharge simulations and local observations of event-specific phenomena. In addition, IFKIS-Hydro incorporates a web-based information platform, which serves as a central hub for the submission and overview of data. Special emphasis is given to local information. This is accomplished particularly by human observers. In medium-scale catchments, discharge forecast models have an increasing importance in providing valuable information. IFKIS-Hydro was developed in several test regions in Switzerland and the first results of its application are available now. The system is constantly extended to additional regions and may become the standard for warning systems in smaller catchments in Switzerland.     

Estimating economic impacts in New Zealand: Technical issues

Abstract: This technical paper describes the techniques used to calculate future economic impacts, using two quite different situations: a technology park in a major urban area and the suspension of fees at a tertiary institution in a provincial town. A number of issues arose which required assumptions to be made. Notable among these were the lack of regionalized input–output tables and estimating the ‘leakage’ to economies outside the specified target area.     

Holocene environmental dynamics of south-eastern Brazil recorded in laminated sediments of Lago Aleixo

Environmental changes of the last 9,300 years were reconstructed by geochemical and pollen analyses of a 14-m-long, laminated sediment core from Lago Aleixo, south-eastern Brazil. Fossil pollen assemblages indicate open savannah vegetation (campo cerrado) and gallery forests until approximately 6,900 cal. BP. During that time, siderite laminae were deposited under anoxic conditions at the lake bottom. Then, increased rainfall and a shorter annual dry period allowed gallery forests and semi-deciduous forests to expand, leading to more closed cerrado vegetation. High-intensity rainfall events during this period are recorded as peaks in K and Ti concentrations. The sediment facies during this period consists of alternating layers of diatoms and minerogenic matter. C/N ratios imply that algae and perhaps soils, too, were the main contributors to sediment organic matter. Biogenic silica and δ¹³C_org variations indicate increasing primary productivity, which was related to higher nutrient flux from intensified leaching of soils, as shown by rising K/Al ratios. Around 800 cal. BP, a closed, semi-deciduous forest developed under present-day climate conditions. Slope stabilization diminished erosion processes in the catchment and caused reduced input of minerogenic matter into the basin. Human impact is evident in the topmost homogeneous sediments, as removal of the stabilizing forest cover amplified soil erosion. The continuous trend to more humid conditions during the Holocene probably reflects increased influence of the Amazon Basin as a moisture source. We conclude that the Lago Aleixo sediment archive was a sensitive recorder of environmental dynamics in tropical South America, which were mainly controlled by changes in precipitation patterns.     

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165?cal.?year BP. The origin of organic matter was established using total-organic?Ccarbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (??¹³C_OM) and nitrogen (??¹⁵N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. >7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165?years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600?cal.?year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the ??¹⁵N and ??¹³C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600?cal.?year BP.     

Landscape governance: The “politics of scale” and the “natural” conditions of places

Governance has become an iridescent concept in recent years. The term is widely used in almost all social-science disciplines as well as in the political process. The intention of this paper is not so much to clarify these sometimes vague meanings but to highlight some characteristics of environmental governance connected with the restructuring of the spatial dimensions of politics. It starts from the assumption that the quest for multi-level decision making is particularly pressing for environmental governance. However, multi-level governance raises concern about the constitution of various spatial levels and their relationships with each other, as discussed under the term of “politics of scale”. Moreover, it is argued that for environmental governance the spatial reference is strongly connected with another challenge, which concerns the question of how to deal with the biophysical conditions of particular places. The term landscape governance is introduced to tackle this question without referring to an ontologically given space. Thus, landscape governance deals with the interconnections between socially constructed spaces (the politics of scale) and “natural” conditions of places. For this task, the concept of societal relationships with nature is introduced and applied to the term “landscape” as a bridging concept between social and natural sciences. The paper illustrates the approach of landscape governance with examples of problem-oriented interdisciplinary research at the UFZ-Centre for Environmental research in Leipzig, Germany.     

A review on missing hydrological data processing

Like almost all fields of science, hydrology has benefited to a large extent from the tremendous improvements in scientific instruments that are able to collect long-time data series and an increase in available computational power and storage capabilities over the last decades. Many model applications and statistical analyses (e.g., extreme value analysis) are based on these time series. Consequently, the quality and the completeness of these time series are essential. Preprocessing of raw data sets by filling data gaps is thus a necessary procedure. Several interpolation techniques with different complexity are available ranging from rather simple to extremely challenging approaches. In this paper, various imputation methods available to the hydrological researchers are reviewed with regard to their suitability for filling gaps in the context of solving hydrological questions. The methodological approaches include arithmetic mean imputation, principal component analysis, regression-based methods and multiple imputation methods. In particular, autoregressive conditional heteroscedasticity (ARCH) models which originate from finance and econometrics will be discussed regarding their applicability to data series characterized by non-constant volatility and heteroscedasticity in hydrological contexts. The review shows that methodological advances driven by other fields of research bear relevance for a more intensive use of these methods in hydrology. Up to now, the hydrological community has paid little attention to the imputation ability of time series models in general and ARCH models in particular.