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

Nikolaos Kamidis,Emmanuil Koutrakis,Georgios Sylaios,Argyrios Sapounidis

doi:10.3390/w13202832

Nikolaos Kamidis, Emmanuil Koutrakis + Show 2 more

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https://doi.org/10.3390/w13202832

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Journal: Water	Publication Date: Oct 12, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: Democritus University of Thrace

Abstract

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.

Highlights

River runoffs are responsible for the transport of 95% of sediments [1], and the introduction of 232–483 × 105 tons of dissolved inorganic phosphorus (DIP) per year, worldwide, into the coastal ocean environment [2,3]
Strong thermal stratification was detected during summer, between 6 and 15 m and from 3 to 9 m depth, for Thissavros and Platanovrisi reservoirs, respectively (Figure 5)
We believe that this work is able to answer the questions that were placed initially regarding the examination of the response of the lower reaches to the construction of the dams in terms of hydrology, hydrochemistry and stoichiometry and the investigation of the water quality alterations inside both dams due to seasonality and climatic conditions

Summary

Introduction

River runoffs are responsible for the transport of 95% of sediments [1], and the introduction of 232–483 × 105 tons of dissolved inorganic phosphorus (DIP) per year, worldwide, into the coastal ocean environment [2,3]. As for dissolved inorganic nitrogen (DIN), it is estimated that the average annual runoff from a relatively undisturbed riparian ecosystem is 100 kg N per km of catchment area, annually [4]. About 50% of river water outflowing to the oceans is passing through dams, a percentage that is expected to increase to 90% by 2030 [5]. This accounts to more than 800,000 operational artificial reservoirs and lakes [6], 75,000 of which are considered large constructions with high storage capacity (surface area < 0.1 km2 ; [7]). According to Maavara et al [8] around 12%

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