Evaporation from the dried-up lake bed of Lake Urmia, Iran.

Lake Urmia in north-western Iran was once one of the world's largest hyper-saline lakes and represented a unique ecosystem for a number of endangered species. The lake's shrinking over the past decades has attracted considerable attention and several studies have addressed its water balance. Yet, evaporation of shallow groundwater from the dried-up lake bed has not been fully quantified - despite the appreciable size of these areas (approx. 4000 km2 in summer 2015). Here, we target this water cycle component by combining column experiments with upscaling and regionalisation techniques. In the experiments, we studied evaporation from two undisturbed soil cores from the exposed lake bed in a climate chamber, mimicking diurnal temperature and humidity variations in the three summer months of the study area. Despite the dropping water levels in the columns and the formation of salt crusts, evaporation rates remained remarkably constant (0.12 and 0.20 mm d-1). This suggests that the system is not driven by slow vapour diffusion, but controlled by capillary rise in the fine-grained sediments, ensuring steady water supply to the column surface. Thus, evaporation from the dried-up lake bed can be assumed to be largely independent from the unsaturated zone thickness (within the observed water level range) and evaporation rates can be simply upscaled and regionalised by considering the satellite-derived development of dried-up lake bed areas (1998-2020). In this time-period, estimated summer evaporation from the exposed lake bed reached maximum values of 0.04 and 0.07 km3 (summer 2015). While these absolute numbers are significant (comparable to the catchment's annual urban drinking water consumption), they correspond to only 4 and 7 % of the evaporation from the open lake surface (1.06 km3).

Climate change or irrigated agriculture - what drives the water level decline of Lake Urmia.

Lake Urmia is one of the largest hypersaline lakes on earth with a unique biodiversity. Over the past two decades the lake water level declined dramatically, threatening the functionality of the lake's ecosystems. There is a controversial debate about the reasons for this decline, with either mismanagement of the water resources, or climatic changes assumed to be the main cause. In this study we quantified the water budget components of Lake Urmia and analyzed their temporal evolution and interplay over the last five decades. With this we can show that variations of Lake Urmia's water level during the analyzed period were mainly triggered by climatic changes. However, under the current climatic conditions agricultural water extraction volumes are significant compared to the remaining surface water inflow volumes. Changes in agricultural water withdrawal would have a significant impact on the lake volume and could either stabilize the lake, or lead to its complete collapse.

The Lake Urmia environmental disaster in Iran: A look at aerosol pollution.

Lake Urmia (LU) once was the second largest hypersaline lake in the world, covering up to 6000km2, but has undergone catastrophic desiccation in recent years resulting in loss of 90% of its area and extensive coverage by playas and marshlands that represent a source of salt and dust. This study examines daily Aerosol Optical Depth (AOD) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2001 and 2015 over northwestern Iran, which encompasses LU. Intriguingly, salt emissions from the LU surface associated with ongoing desiccation do not drive the study region's AOD profile, whereas pollution transported from other regions and emissions around LU are more important. Signatures of increasing local crustal emissions are most evident outside of the peak dust season (January, February, and October) and on the periphery of LU. AOD has generally increased in the latter half of the study period with the onset of the AOD ramp-up starting a month earlier in the spring season when comparing 2009-2015 versus earlier years. Results indicate that suppression of emissions on the LU border is critical as the combined area of salt and salty soil bodies around LU have increased by two orders of magnitude in the past two decades, and disturbing these areas via activities such as grazing and salt harvesting on the lake surface can have more detrimental impacts on regional pollution as compared to benefits. These results have important implications for public health, climate, the hydrological cycle, and pollution control efforts.

Evaluation of permeable pavement responses to urban surface runoff.

The construction of permeable pavement (PP) in sidewalks of urban areas is an alternative low impact development (LID) to control stormwater runoff volume and consequently decrease the discharge of pollutants in receiving water bodies. In this paper, some laboratory experiments were performed to evaluate the efficiency of a PP subjected to sediment loadings during its life span. Simple infiltration models were validated by the laboratory experiments to evaluate the trend and extend of PP infiltration capacity throughout the life of the pavement operation. In addition, performances of the PP in removing total suspended solids (TSS) and selective nutrient pollutants such as NO3-,NH4+ and PO4-3 from the surface runoff have been investigated. Experimental data showed that the PP was completely clogged after seven hydrological years. The model revealed that the ratio of horizontal to vertical hydraulic conductivity is 3.5 for this PP. Moreover, it was found that 20% reduction in hydraulic conductivity occurred after three hydrological years. The PP showed 100%, 23% and 59% efficiencies in sediment retention (TSS removal), (PO4-3), and N-NH4+ removal during the entire study, respectively. However, the removal efficiency of (N-NO3-) was -12% and we suspect the increase in effluent (N-NO3-) is due to the nitrification process in subsurface layers. This study demonstrated that when PPs are annually cleaned, it is expected that PPs can function hydraulically and be able to remove particulate pollutants during their life span by a proper maintenance.

Spatial-temporal assessment and redesign of groundwater quality monitoring network: a case study.

Assessment of groundwater quality monitoring networks requires methods to determine the potential efficiency and cost-effectiveness of the current monitoring programs. To this end, the concept of entropy has been considered as a promising method in previous studies since it quantitatively measures the information produced by a network. In this study, the measure of transinformation in the discrete entropy theory and the transinformation-distance (T-D) curves, which are used frequently by other researchers, are used to quantify the efficiency of a monitoring network. This paper introduces a new approach to decrease dispersion in results by performing cluster analysis that uses fuzzy equivalence relations. As a result, the sampling (temporal) frequency determination method also recommends the future sampling frequencies for each location based on certain criteria such as direction, magnitude, correlation with neighboring stations, and uncertainty of the concentration trend derived from representative historical concentration data. The proposed methodology is applied to groundwater resources in the Tehran-Karadj aquifer, Tehran, Iran.