Impact of River Damming on Downstream Hydrology and Hydrochemistry: The Case of Lower Nestos River Catchment (NE. Greece)

In this paper, a series of field surveys were carried out along the Nestos River watershed (NE Greece) to assess the influence of two hydropower dams (Thissavros and Platanovrisi) upon the hydrology, hydrochemistry and nutrients stoichiometry of the river. Results showed that Nestos hydrology, downstream of the reservoirs, is entirely governed by the man-induced hydropower-driven dam retention/release policy. Dams’ operation increased the retention of dissolved inorganic nitrogen (DIN) and total suspended solids (TSS) significantly, affecting their downstream fluxes, even under water release regime. On the contrary, dams’ construction and operation did not seem to influence the downstream fluxes of dissolved inorganic phosphorus (DIP) and silica (DSi), although these elements also depended on the releasing policy. DIN retention, combined with the dependence of DIP to the water level of Thissavros, resulted in alteration of the N:P ratio at the downstream part. Almost all nutrients were stored at the bottom layer of Thissavros reservoir, especially under the summer stratification regime. Platanovrisi reservoir acts as a buffer zone between Thissavros and the Nestos downstream part. Anoxic conditions in the reservoirs favour the transformation of nitrates into ammonia and the remineralization of phosphorus from sediments, creating a degraded environment for freshwater fauna.

Assessment of Stocking Activities on the Native Brown Trout Populations from Nestos River (Southern Balkans) Inferred by mtDNA RFLP and Sequencing Analyses

Alien fish introductions, conducted towards the ichthyofauna enhancement in local drainages, have been occasionally proved harmful for the indigenous freshwater fish populations. The present study was designed to assess the impact of stocking activities, carried out in the past decades with fingerlings originating from Acheloos river hatcheries, on the native trout (Salmo sp.) populations of Nestos River, Greece. Trout specimens collected from several tributaries of Nestos River and were analyzed by means of PCR-RFLP and sequencing targeting the mitochondrial ND5-ND6 genes and the entire control region, respectively. It should be mentioned that trouts from Acheloos mainly belong to the marmoratus mitochondrial DNA (mtDNA) lineage, while the autochthonous trouts from Nestos belong to the Adriatic lineage. Both methodologies demonstrated that most samples from the three tributaries located at the lower part of Nestos constitute offspring of the fingerlings transferred from Acheloos hatcheries. Therefore, these tributaries have been strongly affected by stocking activities with a potential complete loss of their autochthonous trout. On the other hand, it seems that trout populations from higher altitude tributaries have not been affected by stockings. Hence, efforts should be undertaken in order to prevent the prevalence of the non-indigenous translocated Salmo in higher altitude tributaries, in conjunction with a management plan designed for the total trout populations from the area, speaking of which it has been recently included to the National Park of Rodopi Mountains.

Assessment of Two Adjacent Mountainous Riparian Areas along Nestos River Tributaries of Greece

The riparian areas of the Mediterranean are unique but face many pressures from anthropogenic and climate change impacts. They have very rich and diverse plant communities as a result of the dynamic fluvio-geomorphologic conditions of the Mediterranean streams. In this study, the riparian areas of two adjacent mountainous tributaries (Arkoudorema and Vathirema) of the Nestos River were studied. To assess the condition of riparian areas holistically, diverse measurements are required. This is why fluvio-geomorphologic (in the field and with GIS), vegetation (surveys and visual protocols) and ground-dwelling insect (pitfall traps and indices) measurements were taken along an elevational gradient. The results of all three methodologies draw to similar conclusions, with Vathirema sub-watershed riparian areas being in better condition than Arkoudoreama. This was expected, since Vathirema has less anthropogenic pressures. In addition, the riparian areas in higher elevations were in better condition for the same reason. To implement integrated water resources management plans, fluvio-geomorphologic and biological (e.g., vegetation and insects) datasets are required to provide a holistic view on the watershed and riparian area conditions. For the studied sub-watersheds, we recommend these measurements to continue, to record the current anthropogenic pressures and based on this information to suggest best management practices that will secure long-term sustainability.

Comparison between Calculation and Measurement of Total Sediment Load: Application to Nestos River

Measurements of stream discharge, bed load transport rate and suspended sediment concentration in the Nestos River (northeastern Greece) were conducted by the Section of Hydraulic Engineering, of the Civil Engineering Department, Democritus University of Thrace. In addition to those measurements, the total sediment concentration was calculated by means of the formulas of Yang. The comparison between the calculated and measured total sediment concentration was achieved by means of several statistical criteria and the results were deemed satisfactory.

Parameter Optimization of a Bed Load Transport Formula for Nestos River, Greece

In the Second EWaS International Conference (June 2016, Chania, Crete, Greece), the bed load transport formula of Meyer-Peter and Müller (1948) was calibrated with respect to the bed roughness coefficient for Nestos River. The calibration was manual and incremental, taking five measured values of bed load transport rate at a time. In contrast, the present study carries out a nonlinear optimization of two suitable parameters, while utilizing the average value of the roughness coefficient kst found by the manual calibration. Thus, a uniform calibration is attained, by taking at once the totality of the available 68 measurement points. The results did not show any marked fitting improvement in comparison to the previous study. However, considering moving averages of the measured bed load transport values yields a better adjustment of the model to the measured results.

Soil Erosion, Streambed Deposition and Streambed Erosion—Assessment at the Mountainous Terrain

An Integrated Mathematical Model (IMM) is applied at a continuous time scale in Nestos River basin (Macedonia–Thrace border, northeastern Greece). The IMM comprises a rainfall–runoff submodel, a soil erosion submodel, a streambed deposition submodel and a streambed erosion submodel, and computes sediment yields at the outlet of the basin, at fine time steps and for long periods of time. Soil erosion is estimated by means of the Modified Universal Soil Loss Equation (MUSLE), deposition of sediment load is modeled by the formulas of Einstein and Pemberton and Lara, while streambed erosion is estimated through the formula of Smart and Jaeggi. The application of the IMM enables the computation of annual sediment yields, at the outlet of the basin.