Role of River–Lake System Sediments and Microbial Activity in the Hyporheic Zone

The effect of river–lake systems on the surface water self-purification process is a significant and not fully recognised scientific issue. The conditions prevailing in the hyporheic zone of these ecosystems are of great importance in the process of component exchange between water and sediments. The aim of this study was to investigate the influence of the type of sediments located at the bottom of the riverbed being part of a river–lake system on microbial activity in the hyporheic zone. An ex situ experiment was used to study the microbiological activity and the transformation of components in the collected river sediments. It was found that the specific properties of sediments varied depending on their location in the riverbed between the lakes comprising the system and that the prevailing meteorological conditions can also have an effect on microbial activity in the hyporheic zone, e.g., aerobic conditions. These conditions determined the intensity of component conversion in the sediments due to microbial metabolism. A closer understanding of the processes occurring in the hyporheic zone may allow the processes of water self-purification within river–lake systems to be supported in the future, which will contribute to the improvement of surface water quality.

Changes in zooplankton communities of the Lebyazhye system restored lakes

Ponds rehabilitation projects for the purpose of eco - rehabilitation following significant anthropogenic impacts or degradation are becoming more frequent but not always successful. Therefore, the experience of the restoration of the Lebyazhye system lakes in Kazan city (Russia) is interesting. Previously, the lake system used to consist of four ponds, but due to water catchment area reduction, the area of the lake system also decreased, and only one lake remained. The restoration of the Lebyazhye system lakes was carried out in 2017 and included the deepening of the basin of the Bolshoe and Svetloe Lebyazhye lakes to 4 m, the sealing of the bed of future ponds with bentonite mats, supplying water from Izumrudnoye lake through a pressure water conduit and filling the basin of the lakes with water. The research is devoted to the study of the restoration of zooplankton communities in the Lebyazhye system lakes. For this purpose, the indicators of zooplankton communities before and after eco-rehabilitation measures were compared. After the implementation of eco-rehabilitation measures, significant changes in environmental parameters were observed: the salinity of water decreased, the oxygen content in the water, pH increased. In zooplankton communities, the species richness and diversity increased, new species appeared, as well as those that lived in the lake system earlier before eco-rehabilitation measures were taken.

Hydrological System of the Plitvice Lakes—Trends and Changes in Water Levels, Inflows, and Losses

The Plitvice Lakes National Park is inscribed on UNESCO’s World Heritage List. The lake system is composed of 16 cascading lakes of different sizes separated by tufa barriers, which are the park’s key phenomenon. The lakes are characterized by highly diverse trends of the characteristic hydrological indicators—mean annual water levels, discharges, and tufa barrier growth. The analyses carried out in this paper identified that in the period before the early 1990s, Kozjak Lake had a trend of decreasing discharges, together with a trend of increasing water levels and growing tufa barriers. In contrast to this, in the period after 2001, a trend of increasing discharges was recorded, as well as a trend of decreasing water levels and decreasing tufa barriers. A potential cause of the barriers decreasing in size were the extremely high discharges during the last decade, which resulted in increased erosion of the tufa barriers. Losses of water due to the sinking from the lake system as well as the upper Korana course were confirmed, and it was identified that during the analyzed period the losses had not changed significantly. It was determined that the losses of water from Kozjak Lake occurred during low-water periods; however, they depended not only on the quantity of water flowing through the lakes but also on the hydrological conditions underground. The analyses carried out and the methodological procedures used in the analyzed area of the Plitvice Lakes are useful examples for the performance of analyses at similar lakes in karst formed by tufa deposition processes.

The Paleomorpholigic Conditions of the Formation of the Settlement of Shitkino (Northwest Russia)

Для многих раннесредневековых памятников Северо-Запада Европейской России палеогеографические условия реконструированы недостаточно. При этом географический контекст развития поселений играет важную роль в исторической и экономической жизни людей Средневековья на локальном уровне. Археологический памятник поселение Шниткино расположен в бассейне Западной Двины на западном макросклоне Валдайской возвышенности. Изучаемое поселение находится на берегу озера Шнидкино, через которое насквозь протекает река Торопа. Используя геолого-геоморфологические методы, авторы статьи описали строение озерной террасы и озерно-речной поймы, в которых был найден культурный слой IX–X веков и отдельные археологические артефакты. Седиментационные архивы торфа, озерных, аллювиальных и склоновых отложений, продатированные радиоуглеродным методом, позволили оценить, насколько рельеф раннего Средневековья отличался от современного, и определить возможную функциональность территории во время существования поселения. Выявленные стабильность берега и аккумулятивная динамика озерно-речной системы свидетельствуют о том, что за последние несколько тысяч лет форма берега почти не изменилась. Речные и озерные террасы с похожей динамикой, обнаруживаемые в бассейне реки Торопы, считаются наиболее привлекательными позициями для поселенцев раннего Средневековья. The palaeomorphology of many early medieval monuments in Northwest Russia has not been reconstructed yet. In historical and economic perspective, the geographical location has a great impact on settlement formation and affects people’s lives significantly. The settlement of Shitkino is an archaeological monument situated in the basin of the Western Dvina at the western slope of the Valdai Hills. The settlement of Shitkino is located at the shore of Shnidkino lake, which is traversed by the Toropa River. The authors of the article employ geological and geomorphological analyses to explore the floodplain and its fluvial terraces, to make archaeological finds and to gain evidence of the events of the 9th–10th centuries. The method of radiocarbon dating enabled the scientists to estimate the age of peat sediments, fluvial and slope deposits, to estimate the degree of relief transformation and to tentatively assess the extent of the functionality of the land in medieval times. The accumulated data, such as the structural stability of the shore and the dynamics of the river-lake system show that during the recent thousands of years the shores of the lake have been only insignificantly transformed. It is believed that in the early middle ages people preferred to settle in the basin of the Toropa River.

Desiccation of the Transboundary Hamun Lakes: Natural or Anthropogenic?

This paper investigates the hydrologic and water management reasons behind the desiccation of the Hamun Lakes in the Iran-Afghanistan border region. We analysed changes in Hirmand (or Helmand) River flow, the main tributary providing 70% of the lakes’ total inflow, and precipitation during 1960-2016 by calculating standardized indices for precipitation (SPI) and discharge (SDI). Also, we applied Normalized Difference Spectral Indices (NDSIs) using satellite images from 1987 to present to observe monthly areal change of the lakes. The transboundary water body is responding to changes in regional water management, which has severely reduced the lakes’ inflow. Upstream water regulation in Afghanistan coupled with reservoir construction on the Iranian side has caused nearly full desiccation of major parts of the lake system. There is a discernible shift in the relation between the Hirmand River flow at the international border and upstream precipitation over the lakes’ basin before and after 2004. From 1960 to 2003, high river flows were expected to feed the lakes due to high precipitation over the basin. However, the Hirmand River flow at the border declined after 2004 despite large amounts of upstream precipitation, including the largest recorded amounts, especially in the Hindu Kush mountains. Further, environmental water stress caused by anthropocentric water management in Iran by reservoir construction has impacted the area of the lakes. Although a long period of drought from 1998-2004, i.e. climatic driver, decreased the lakes’ area, the lake system is primarily falling victim to anthropogenic flow alterations in the transboundary river basin. The lakes’ shrinkage places socio-economic stress on an already-vulnerable region with important public health implications as the exposed lake beds turn into major sources of sand and dust storms.