Consistency of thresholds for eutrophication assessments, examples and recommendations

International harmonisation of management goals for eutrophication processes in coastal waters, requiring reduction of discharges and depositions of nutrients and organic matter, needs coordinated assessments and measures. This is especially necessary in open areas, connected by currents and mixing processes with trans-boundary exchanges. Management goals, defined nationally as local thresholds for nutrients and chlorophyll-a, had been applied recently (2006–2014) within international eutrophication assessments in the North Sea (OSPAR) and Baltic Sea (HELCOM). Consistency of thresholds for nitrogen nutrients and chlorophyll-a concentrations is tested by mixing diagrams and correlations between nitrogen nutrients (total and inorganic nitrogen) and chlorophyll-a. Results indicate mean consistent relations, but single deviations as in the continental coastal water of the North Sea surpassed means by a factor up to 5 for chlorophyll-a in relation to inorganic nitrogen. Thresholds differed across national borders significantly. Correlations of thresholds and assed data reflect the degree of regional deviations by comparison. Consistency of regionally applied thresholds can be achieved stepwise, by application of regionally correlated means, by adaptation to mixing and parameter relations, and finally by relations of thresholds to natural background concentrations. By this, consistency of international assessments can be improved generally, allowing coordinated management of open coastal waters.

Cloud microphysical structure analysis based on high-resolution insitu measurements

This study investigates the microphysical parameters and shapes of droplet size distributions (DSDs) along three aircraft traverses of developing convective clouds during Cloud Aerosol Interactions and Precipitation Enhancement EXperiment (CAIPEEX) 2015 at a sampling frequency of 25 Hz. The droplet number concentration (Nc, cm−3), and liquid water content (LWC, gm−3) present steep gradients within a few tens of meters’ zones near the cloud edges and relatively gentle gradients in the strong updraft zones. Sometimes, the horizontal LWC distribution resembles a trapezoid-like shape with steep LWC and Nc gradients near the cloud edges. The LWC maximums (LWCmax) are lower than the adiabatic LWC, but the high adiabatic fractions in the cloud core indicate low dilution. High LWC/LWCmax, largest droplets, and narrow and similarly-shaped DSDs are found in the regions of high updrafts. Zones of low LWC/LWCmax are found close to the cloud edges, where DSDs are highly diverse, containing both large and small droplets. Finally, we analyze the mixing diagrams.Significant in-phase turbulent fluctuations in LWC and Nc were found. The effective radii change slightly across cloud updraft zones but decrease at the low LWC/LWCmax ratio zone close to cloud edges. The spectra of LWC and Nc obey Kolmogorov -5/3 turbulence law. The radii of the correlation of LWC and Nc in updraft zones are of several tens of meters. Filaments up to 120-175 m in size are also noticed.

Using Si, Al and Fe as Tracers for Source Apportionment of Air Pollutants in Lake Baikal Snowpack

The aim of this study was to select chemical species characterized by distinctly different proportions in natural and anthropogenic particulate matter that could be used as tracers for air pollutant sources. The end-member mixing approach, based on the observation that the chemical species in snow closely correlated with land use are those that exhibit differences in concentrations across the different types of anthropogenic wastes, was used for source apportionment. The concentrations of Si and Fe normalized to Al were used as tracers in the mixing equations. Mixing diagrams showed that the major pollution sources (in descending order) are oil, coal, and wood combustion. The traces of several minor sources, such as aluminum production plants, pulp and paper mills, steel rust, and natural aluminosilicates, were also detected. It was found that the fingerprint of diesel engines on snow is similar to that of oil combustion; thus, future research of the role of diesel engines in air pollution will be needed. The insufficient precision of source apportionment is probably due to different combinations of pollution sources in different areas. Thus, principles for the delineation of areas affected by different source combinations should be the subject of further studies.

Theoretical analysis of mixing in liquid clouds – Part IV: DSD evolution and mixing diagrams

Evolution of droplet size distribution (DSD) due to mixing between cloudy and dry volumes is investigated for different values of the cloud fraction and for different initial DSD shapes. The analysis is performed using a diffusion–evaporation model which describes time-dependent processes of turbulent diffusion and droplet evaporation within a mixing volume. Time evolution of the DSD characteristics such as droplet concentration, LWC and mean volume radii is analyzed. The mixing diagrams are plotted for the final mixing stages. It is shown that the difference between the mixing diagrams for homogeneous and inhomogeneous mixing is insignificant and decreases with an increase in the DSD width. The dependencies of the normalized cube of the mean volume radius on the cloud fraction were compared with those on normalized droplet concentration and found to be quite different. If the normalized droplet concentration is used, mixing diagrams do not show any significant dependence on relative humidity in the dry volume. The main conclusion of the study is that traditional mixing diagrams cannot serve as a reliable tool for analysis of mixing type.

Seasonal variations in the water quality of six tropical micro- and mesotidal estuaries along the central west coast of India

Seasonal nutrient dynamics were investigated in four rivers with a microtidal range (Terekhol, Chapora, Sal and Talpona rivers) and were compared with those of two rivers with a mesotidal range (Zuari and Mandovi rivers) along the central west coast of India. Rainfall and freshwater discharge during the wet season led to salinity stratification of the water columns at the mouths of these rivers. Nutrient concentrations in all rivers were higher during the wet season than in the dry season due to considerable land run-off. Based on the estuarine mixing diagrams of the nutrients with regard to salinity, the mesotidal rivers showed greater flushing capacity and acted as corridors for the passage of nutrients between the estuary and open ocean. Conversely, of the microtidal rivers, the Terekhol and Chapora seemed to retain nutrients, whereas there was no indication of the presence of a nutrient sink or source in the Talpona River. The Sal River was eutrophic with high nutrient levels and acted as a source of phosphorus and nitrogen. Thus, the present study clearly illustrates the important role played by minor river estuaries in modifying nutrient concentrations during their transport from rivers to coastal waters and vice versa.

Theoretical analysis of mixing in liquid clouds. Part IV: DSD evolution and mixing diagrams

Evolution of droplet size distribution (DSD) due to mixing between cloudy and dry volumes is investigated for different values of the cloud fraction and different initial DSD shapes. The analysis is performed using a diffusion-evaporation model which describes time-dependent processes of turbulent diffusion and droplet evaporation within a mixing volume. Time evolution of the DSD characteristics such as droplet concentration, liquid water content, mean volume and the effective radii is analyzed. The mixing diagrams are plotted for the final mixing stages. It is shown that the difference between the mixing diagrams for homogeneous and inhomogeneous mixing is insignificant and decreases with an increase in the DSD width. The dependencies of normalized cube of the effective radius on the cloud fraction were compared with those on normalized droplet concentration and found to be quite different. In case the normalized droplet concentration is used, mixing diagrams do not show any significant dependency on relative humidity in the dry volume. The main conclusion of the study is that traditional mixing diagrams cannot serve as a reliable tool in analysis of mixing type.

On the Deceiving Aspects of Mixing Diagrams of Deep Cumulus Convection

Mixing processes in deep precipitating cumulus clouds are investigated by tracking Lagrangian particles in a large-eddy simulation. The trajectories of particles are reconstructed and the thermodynamic properties of cloud air are studied using mixing diagrams. The trajectory analysis shows that the in-cloud mixing is entirely dominated by lateral entrainment and that there is no significant vertical mixing by downdrafts originating from cloud top. Yet the thermodynamic properties of the particles are located close to a line in the mixing diagrams, which appears to be consistent with two-point vertical mixing. An attempt is made to resolve this paradox using the buoyancy-sorting model of Taylor and Baker, but it is found that this model does not provide a full explanation for the location of particles in the mixing diagram. However, it is shown that the mixing-line behavior can be well understood from a simple analytically solvable model that uses a range of different lateral entrainment rates. Two further factors that determine the location of particles in the mixing diagram are identified: the removal of noncloudy air and precipitation effects. Finally, a thermodynamic argument is given that explains the absence of coherent downdrafts descending from cloud top.

Exploring runoff processes using chemical, isotopic and hydrometric data in a discontinuous permafrost catchment

Hydrometric, isotopic and hydrochemical data were used to investigate runoff generation in a discontinuous permafrost headwater catchment. Research was undertaken between 10 April and 8 July 2008 within Granger Basin, a 7.6 km2 sub-catchment of the Wolf Creek Research Basin, Yukon Territory, Canada. The objectives of this research were to utilize hydrometric, stable isotope and hydrochemical methods to: (i) establish water balance components and (ii) couple water balance information with stable isotope and hydrochemical information to provide an enhanced understanding of runoff sources and pathways. The water balance components were snowmelt (152 mm), precipitation (68 mm), evaporation (88 mm), discharge (173 mm) and change in storage (−41 mm). The runoff ratio was high compared with previous years in this catchment. Using two-component hydrograph separation, pre-event water represented ∼73% of total discharge during freshet. End-member mixing diagrams suggested three contributing sources to streamflow in the following order: groundwater, soil water and snowmelt water. Concentration versus discharge diagrams identified the dilution of weathering ions during melt, while the ratio of potassium to calcium in streamwater suggests early contributions of pre-event water to discharge. Results from this research support previous work that pre-event water dominates freshet, yet the role of deeper groundwater is highlighted as an important contribution.