Impact of small hydropower plants on physicochemical and biotic environments in flatland riverbeds of LithuaniaPublicationThe impact of a small hydropower plant (SHP) on river water quality and macroinvertebrates has been investigated in 5 Lithuanian rivers and involved 17 dams, ten of which are in a sequence in the same river system. The hydrostatic head of SHP dams ranged from 2.75 to 14.50 m and the capacities of their reservoirs varied from 40×103 to 15,500×103 m3. Physicochemical characteristics, as well as macroinvertebrate communities, were evaluated in sites above and below the SHP dams comparing them with reference sites. It was established that construction of SHP dams (H<15 m) in Lithuania substantially changed regimes of suspended solids, fine particles and nutrients only locally regardless of hydrostatic head of the dam. Compared to reference sites, SHP reservoirs and sites below SHP dams had relatively more Chironomidae larvae and Oligochaeta, and less Coleoptera larvae as well as the relative abundance of pollution-sensitive Ephemeroptera and EPT. Water quality according to biotic indexes (DSFI and HBI) in the sites influenced by SHP dams was recognised to be moderate or poor, but impact was only local. This suggests that increment of catchment’s area and intensive land use for agriculture within the river basin plays more important role than SHP dams. 63 139
- research articleJournal of water security / Aleksandras Stulginskis university, Riga Technical University. , 2015, vol. 1, p. 14-24In spite of the many investigations that have been conducted on turbulent flows, the generation and development of turbulent vortices has not been investigated sufficiently yet. This prevents to understand well the processes involved in the flow. That is unfavorable for the further investigations. The developing vortex structures are interacting, and this needs to be estimated. Physical summing of velocities, formed by all structures, can be unfavorable for investigations, therefore they must be separated; otherwise bias errors can occur. The difficulty for investigations is that the widely employed Particle Image Velocity (PIV) method, when a detailed picture of velocity field picture is necessary, can provide photos covering only a short interval of flow, which can’t include the largest flow structures, i.e. macro whirlpools. Consequently, action of these structures could not be investigated. Therefore, in this study it is tried to obtain the necessary data about the flow structure by analyzing the instantaneous velocity measurements by 3D means, which lasts for several minutes, therefore the existence and interaction of these structures become visible in measurement data. The investigations conducted in this way have been already discussed in the article, published earlier. Mostly the generation and development of bottom vortices was analyzed. In this article, the analysis of these turbulent velocity measurements is continued and the additional data about the structure of turbulent vortices is obtained.
19 52 Adsorption of paraquat dichloride to kaolin particles and to mixtures of kaolin and hematite particles in aqueous suspensionsPublicationresearch article ;Martins, Dina Alexandra ;Simões, ManuelMelo, LuísJournal of water security, 2015, vol. 1, p. 25-36Deliberate contamination with pesticides is a potential risk to water security, due to the availability of these contaminants and the fact that they do not need special expertise to handle or apply. Adsorption of the herbicide paraquat from an aqueous solution to suspended particles of kaolin and kaolin/hematite mixture was investigated by kinetic and equilibrium assays, taking into consideration several parameters such as initial pH, sorbent dosage and agitation speed. The results showed that the adsorption process is quite fast, reaching an 18% reduction in paraquat concentration in a very short period of time. The addition of hematite particles to kaolin suspension had no apparent effect on the maximum amount of paraquat adsorbed. Kinetic parameters were determined by fitting the pseudo-second order model to the experimental data (correlation coefficients close to 1). Isotherm studies indicate an inhibitory effect, promoted by hematite particles, that was not detected in the adsorption assays. Equilibrium data was best adjusted using the Langmuir model which yielded higher correlation coefficient values and smaller normalized standard deviations. 16 56
- research article
;Klõga, MarijaMaharjan, BharatJournal of water security, 2015, vol. 1, p. 37-45The nutrient content in streams and rivers depend on many interacting processes such as hydro-geographical conditions and land use practices. The aim of this study was to investigate the current status of Estonian rivers and determine any trends in the concentrations of total nitrogen (TN) and nitrate-nitrogen (NO3 -N) between 1992 and 2013. This study involved 43 monitoring sites and 32 rivers in Estonia. The temporal trends were assessed using the partial MannKendall (PMK) test, which was adapted to account for the influence of water discharge. Most of the studied streams and sites did not show any trend in nitrogen concentrations. The statistically significant downward trend in TN was identified at 13 monitoring stations and upward trend at four monitoring sites. The results for NO3 -N showed a statistically significant downward trend at three sampling sites while the upward trend was found at nine monitoring stations, particularly at four sites located within the nitrate vulnerable zone (NVZ). Overall, the increasing nitrate content in surface waters can most probably be attributed to the intensification of agricultural activities in rivers catchments during the last ten years. However, there are still many uncertainties in nutrient loss processes. Thus, the national monitoring programmes should be further developed. 12 36 Phosphorus removal in a vertical flow constructed wetland using dolomite powder and chippings as filter mediaPublicationDifferent kinds of natural and artificial filter media are able to retain phosphorus in the constructed wetlands. Due to the fact that the constructed wetland needs huge amounts of the filter media, it is very important to find locally available material which distinguishes itself by its ability to retain phosphorus. The materials found in Lithuania were considered and dolomite was chosen. Two dolomite fractions, dolomite powder (1–2 mm) and dolomite chippings (2–5 mm), and sand media were used in the laboratory- scale installed for the comparative experiments. The laboratory-scale with dolomite as the filter media was on average by 21% more efficient in total phosphorus removal in comparison with the sand media. Based on the laboratory research pilot–scale vertical flow constructed wetland of 160 m2 was installed and planted with reed Phragmites australis. The dolomite chippings as filter media were chosen in order to avoid the danger of the clogging of constructed wetland. Efficiency of total phosphorus removal in the pilot-scale vertical flow constructed wetland was on average 95.7%, phosphates removal – 94.8% within one year. 62 102