Denitrification across landscapes and waterscapes: a synthesis.

Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled. In aquatic ecosystems, N inputs influence denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves. Spatially distributed global models of denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing denitrification in a downstream direction exist, including significant denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much denitrification at the watershed scale, per-area denitrification rates in soils and groundwater (kg N x km(-2) x yr(-1)) are, on average, approximately one-tenth the per-area rates of denitrification in lakes, rivers, estuaries, continental shelves, or OMZs. A number of potential approaches to increase denitrification on the landscape, and thus decrease N export to sensitive coastal systems exist. However, these have not generally been widely tested for their effectiveness at scales required to significantly reduce N export at the whole watershed scale.     

Soil lead (Pb) in residential transects through Lubbock,Texas: a preliminary assessment

Residential lead (Pb) contamination, resulting from decades-long use of leaded gasoline and lead-based paint, is likely to be present in soils in most urban areas. A screening level sampling effort demonstrated that Lubbock, Texas, USA, like other cities of its age and size, has areas of elevated soil Pb. This effort was based on soil sampling performed on residential, commercial and thoroughfare properties. The focus of this study was to investigate that component of soil contamination due to combustion of leaded gasoline. Soils were collected from the 1–2 cm surface layer from street-side property borders, well away from buildings that might lead to soil contamination from leaded paint chips. All samples were analyzed for Pb after a 1 M HNO₃ mild extraction to determine the amount of bioavailable Pb. Two of three transects through the city demonstrated significant trends of decreasing Pb concentrations with distance from the city center, paralleling a decrease in developed property age. Peak soil Pb concentrations outside city development was 4.9 ± 0.6 mg/kg while the median concentration for the city was 35.4 mg/kg. Peak soil Pb concentrations in the city center ranged from 90.0 to 174.0 mg/kg and decreased exponentially to 6.0–9.0 mg/kg at the furthest terminus of the residential transects.     

Repeated training does not improve the path integrator in desert ants

Desert ants, Cataglyphis fortis, return to their nest by means of path integration vectors. By using the reversal of these vectors, they approach previously visited feeding sites again. They adjust these vectors whenever outbound and inbound vector are set into conflict or when they make use of external cues. Here, we examine the influence of repeated training on the accuracy, precision, and straightness of outbound and inbound vectors. We trained desert ants to forage to and fro between their nest and a feeder and made sure that they relied exclusively on their path integrator. Neither the ants’ outbound nor their inbound runs, which, in general, are straighter than the outbound runs, become more accurate, precise, or straighter during repeated training. Hence, repeated training does not improve the path integrator in desert ants.     

Impact of climate change on soil moisture dynamics in Brandenburg with a focus on nature conservation areas

Global warming impacts the water cycle not only by changing regional precipitation levels and temporal variability, but also by affecting water flows and soil moisture dynamics. In Brandenburg, increasing average annual temperature and decreasing precipitation in summer have already been observed. For this study, past trends and future effects of climate change on soil moisture dynamics in Brandenburg were investigated, considering regional and specific spatial impacts. Special Areas of Conservation (SACs) were focused on in particular. A decreasing trend in soil water content was shown for the past by analyzing simulation results from 1951 to 2003 using the integrated ecohydrological model SWIM [Krysanova, V., Müller-Wohlfeil, D.-I., Becker, A., 1998. Development and test of a spatially distributed hydrological/water quality model for mesoscale watersheds. Ecol. Model. 106, 261–289]. The trend was statistically significant for some areas, but not for the entire region. Simulated soil water content was particularly low in the extremely dry year 2003. Comparisons of simulated trends in soil moisture dynamics with trends in the average annual Palmer Drought Severity Index for the region showed largely congruent patterns, though the modeled soil moisture trends are characterized by a much higher spatial resolution. Regionally downscaled climate change projections representing the range between wetter and drier realizations were used to evaluate future trends of available soil water. A further decrease of average available soil water ranging from −4% to −15% was projected for all climate realizations up to the middle of the 21st century. An average decrease of more than 25 mm was simulated for 34% of the total area in the dry realization. Available soil water contents in SACs were generally higher and trends in soil moisture dynamics were lower mainly due to their favorable edaphic conditions. Stronger absolute and relative changes in the simulated trends for the past and future were shown for SACs within Brandenburg than for the state as a whole, indicating a high level of risk for many wetland areas. Nonetheless, soil water content in SACs is expected to remain higher than average under climate change conditions as well, and SACs therefore have an important buffer function under the projected climate change. They are thus essential for local climate and water regulation and their status as protected areas in Brandenburg should be preserved.     

Conservation perspectives of small-scale private forest owners in Europe: A systematic review

Private forest owners are the main forest ownership group within Europe, and important conservation values have been found on their land. Yet, small plot sizes, societal heterogeneity, and structural changes impede developing and implementing effective conservation programs in private forests. We present a systematic literature review focusing on small-scale private forest owners and their perspectives on nature conservation by synthesizing research approaches, social-ecological drivers, and policy recommendations. Conservation perspectives were positively related to female gender, higher levels of education, formalized forest management, an active relation to the forest, and ecological values of the property. In contrast, high age, rural orientation, economic forest management factors, large parcel size, and economic and sentimental property values negatively influenced conservation perspectives. Applying a natural resource conflict management framework, we synthesized recommendations covering three dimensions: substance, procedure, relationship. Considering perspectives of small-scale private forest owners in current forestry decision-making has great potential to strengthen sustainable forest management that integrates nature conservation and resource use.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01615-w.     

über die Notwendigkeit der wirkungsorientierten Analytik in einer umfassenden Wasserforschung

Ohne Zusammenfassung Verantwortliche Herausgeber: Jan Schwarzbauer · Peter Heininger · Evelyn Claus

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Changes in the spatial patterns of human appropriation of net primary production (HANPP) in Europe 1990–2006

Understanding patterns, dynamics, and drivers of land use is crucial for improving our ability to cope with sustainability challenges. The human appropriation of net primary production (HANPP) framework provides a set of integrated socio-ecological indicators that quantify how land use alters energy flows in ecosystems via land conversions and biomass harvest. Thus, HANPP enables researchers to systematically and consistently assess the outcome of changes in land cover and land-use intensity across spatio-temporal scales. Yet, fine-scale HANPP assessments are so far missing, an information important to address site-specific ecological implications of land use. Here, we provide such an assessment for Europe at a 1-km scale for the years 1990, 2000, and 2006. The assessment was based on a consistent land-use/biomass flow dataset derived from statistical data, remote sensing maps, and a dynamic global vegetation model. We find that HANPP in Europe amounted to ~43 % of potential productivity, well above the global average of ~25 %, with little variation in the European average since 1990. HANPP was highest in Central Europe and lower in Northern and Southern Europe. At the regional level, distinct changes in land-use intensity were observed, most importantly the decline of cropland areas and yields following the breakdown of socialism in Eastern Europe and the subsequent recovery after 2000, or strong dynamics related to storm events that resulted in massive salvage loggings. In sum, however, these local dynamics cancelled each other out at the aggregate level. We conclude that this finding warrants further research into aspects of the scale-dependency of dynamics and stability of land use.     

Does quinone or phenol enrichment of humic substances alter the primary compound from a non-algicidal to an algicidal preparation?

Dissolved organic matter (DOM) has been shown to affect phytoplankton species directly. These interactions largely depend on the origin and molecular size of DOM and are different in prokaryotes and eukaryotes. In a preceding study, however, two humic substance preparations did not adversely affect coccal green algae or cyanobacterial growth even at high concentrations of dissolved organic carbon (DOC). These results contradicted previous findings, showing a clear, negative response of different phototrophs to much lower DOC concentrations. To test whether or not at least defined building blocks of humic substances (HSs) are effective algicidal structures, we enriched two humic preparations with hydroquinone and p-benzoquinone, respectively, and exposed two different green algae, Pseudokirchneriella subcapitata and Monoraphidium braunii, and two cyanobacterial species, Synechocystis sp. and Microcystis aeruginosa, to the unmodified and enriched HSs. As response variables, growth rates in terms of biomass increase, chlorophyll-a content, and photosynthetic yield were measured. The highest concentration (4.17 mM DOC) of the modified HSs clearly inhibited growth; the cyanobacterial species were much more sensitive than the green algal species. However, realistic ecological concentrations did not adversely affect growth. Aerating the exposure solution for 24 h strongly reduced the inhibitory effect of the modified HSs. The algicidal effect was obviously caused by monomers and not by polymerised high molecular weight HSs themselves. Furthermore, the maximum quantum yield (Φ PSII max) was stimulated in the green algal species by low and medium DOC concentrations, but reduced in the cyanobacterial species upon exposure to higher HS concentrations. The quinone- and phenol-enriched HSs only showed algicidal activity at high concentrations of 4.17 mM DOC and lost their effects over time, presumably by oxidation and subsequent polymerisation. This study confirms that the applied humic substances themselves are not effective algicides even if enriched in effective structures.