Understanding coastal wetland conditions and futures by closing their hydrologic balance: the case of the Gialova lagoon, Greece

Abstract

Abstract. Coastal wetlands and lagoons are under pressure due to competing demands for freshwater resources and climatic changes, which may increase salinity and cause a loss of ecological functions. These pressures are particularly high in Mediterranean regions with high evaporative demand compared to precipitation. To manage such wetlands and maximize their provision of ecosystem services, their hydrologic balance must be quantified. However, multiple channels, diffuse surface water exchanges, and diverse groundwater pathways complicate the quantification of different water balance components. To overcome this difficulty, we developed a mass balance approach based on coupled water and salt balance equations to estimate currently unknown water exchange fluxes through the Gialova lagoon, southwestern Peloponnese, Greece. Our approach facilitates quantification of both saline and freshwater exchange fluxes, using measured precipitation, water depth and salinity, and estimated evaporation rates over a study period of 2 years (2016–2017). While water exchanges were dominated by evaporation and saline water inputs from the sea during the summer, precipitation and freshwater inputs were more important during the winter. About 40 % and 60 % of the freshwater inputs were from precipitation and lateral freshwater flows, respectively. Approximately 70 % of the outputs was due to evaporation, with the remaining 30 % being water flow from the lagoon to the sea. Under future drier and warmer conditions, salinity in the lagoon is expected to increase, unless freshwater inputs are enhanced by restoring hydrologic connectivity between the lagoon and the surrounding freshwater bodies. This restoration strategy would be fundamental to stabilizing the current wide seasonal fluctuations in salinity and maintain ecosystem functionality but could be challenging to implement due to expected reductions in water availability in the freshwater bodies supporting the lagoon.

Status and Distribution of Waterbirds in a Natura 2000 Area: The Case of Gialova Lagoon, Messinia, Greece

“…Due to man-made constructions over a period of seventy years, the GLw-Natura2000 area has been divided into sub-areas, with different characteristics ( Table 2). At the east of GLw-Natura2000 area, the Tyflomitis artesian springs (a 0.072 Km 2 aquatic habitat covered with reeds) provide freshwater inputs in this area (Manzoni et al, 2020). The Tyflomitis area was once connected to the wetland, but at present it is separated from it via a dike which diverts most of the up-welling groundwater to the sea (Maneas et al, 2019).…”

“…Salt meadows at the fringes, and few embankments (creating small parallel islands) covered by halophytes are found at the north. High salinity fluctuations on an annual basis (Manzoni et al, 2020).…”

“…North wetland (Nw) 0.444 Salt meadows which neighbor cultivations at the north, separated by relative deep drainage channels (with a maximum depth of 1.4 m in winter) within which some reeds remain today. High salinity fluctuations on an annual basis (Manzoni et al, 2020).…”

“…This may make a stop at GLw not as important as it may be in spring, when the wetland may be the first wetland that the birds encounter. In addition, during spring, increased volumes of freshwater due to precipitation and inflows from the catchment, result in lower salinity values and wider expansion of aquatic habitats compared to autumn conditions (Manzoni et al, 2020), making the whole area a more suitable habitat for resting and feeding.…”

“…Apart from limitations in vegetation expansion, salinity values are critical for benthic communities (Newton et al, 2014) and fish (Zoulias et al, 2017), which are vital in the food chain for several waterbirds. At present, fresh water availability is affected by inland human activities, and the wetland is currently lacking fresh water inputs (Maneas et al, 2019;Manzoni et al, 2020). Waste waters from the olive-oil industry pollute surface water bodies (which could flow into the wetland, but currently flow into the sea), while increased irrigation needs in agriculture, and water demand for domestic use limit the amount of available groundwater resources during summer (Maneas et al, 2019).…”