Water budget of a Ramsar site in Ecuador

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Introduction Wetlands play an important role in water quality enhancement, wildlife habitat, water retention during storms, shoreline protection, carbon storage, and providing cultural and recreational resources [1-4]. Unfortunately, wetland areas have been degrading and disappearing rapidly. They are often subjected to several anthropogenic impacts, such as direct discharge of domestic and industrial wastewater, agricultural runoff and sewage, land conversion, pollution, overgrazing, and future degradation is expected to continue [5-9]. Analyzing wetland water inflows and outflows components (i.e. water budget) is essential for understanding how wetlands respond to variations in flows and environmental conditions and how these changes influence the biota, nutrients concentration and distribution, organic matter, soil biochemistry, sediments and physicochemical parameters of the water [10-12]. This analysis allows to assess and forecast wetlands behavior in terms of quantity in order to develop and implement plans for managing and protecting wetlands [13] by the governments, decision-makers and ecologists. Ecuador has 19 wetlands that belong to the Ramsar convention, they possess international status for protection and rational use of their resources [14]. La Tembladera wetland is one of these Ramsar sites since 2011 [15]. This unique ecosystem is located in the coast region of Ecuador and is mainly used for cattle grazing, short-cycle crops, pasture grasses and recreational activities [15; 16]. Besides, La Tembladera is the habitat for 43 plants species, 80 waterfowl birds, 14 fish species, 8 reptiles and 20 mammals. It harbors vulnerable and endangered species and 24 waterfowl endemic species [15]. However, this ecosystem is also facing pressure from anthropogenic activities, specifically, domestic wastewater discharge, agricultural runoff, discharge of urine and faeces produced by Brahman and Brownsuiz cattle, and water control structures (i.e. dams and canals) [16]. These factors influence the quality and quantity of the hydrologic variables as well as the ecological functioning of the wetland [17]. Despite the recognition of La Tembladera as a Ramsar site, studies aimed at the assessment of hydrologic variables are scarce. In general, hydrology research is a complex task due to the various processes involved [18; 19] and the lack of financial support for investigating and estimating all processes that control wetland hydrologic behavior. Low scientific productivity is a crucial issue that affects most of the developing countries in Latin America, including Ecuador because of the economy instability and other factors [20]. The empirical water balance method can be a feasible tool for assessing wetlands hydrologic balance because requires available input data, such as hydro-meteorological data and parameters representing the soil and vegetation characteristics of aquatic ecosystems catchments. This method is simple and widely applied [6; 18; 21-23]. Thus, the present study proposes a water budget estimation during a two-year period in La Tembladera wetland by using the water balance method. Materials and methods Study site La Tembladera wetland is a continental-type freshwater wetland located in the southwestern coast of Ecuador, canton Santa Rosa, province El Oro (3° 29' 26" S, 79° 59' 43" W; 12-18 m a.s.l) (Figure 1). The region has a tropical climate, which is characterized by a wet season (winter) and a dry season (summer). The average annual precipitation is 250-500 mm. The air temperature ranges between 24°C and 26°C [15]. The water body area occupies 1,471.19 ha, its permanent water area is 104 ha. The flooded area depends on the season, the water surface may reach 188 ha during the wet season, and the land surface 1,199 ha. The wetland monthly average water temperature is 25.82°C. During the wet season, the wetland annual average flow rate is 14.50 m3/s, the monthly maximum is 61.0 m3/s and the minimum 0.20 m3/s. The flow rate is usually 0 m3/s during the dry season [15]. Figure 1. The location of La Tembladera wetland in Ecuador (left) and the wetland area boundaries (right) La Tembladera wetland (Figure 2) belongs to the life zone Tropical Spiny Mountain (Monte Espinoso Tropical). For much of the year the wetland water table is near the land surface, hence the vegetation is adapted to moisture conditions, for instance, water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes), common cattail (Typha latifolia) and white lotus (Nymphaea lotus) [25]. Un barco en medio del campo Descripción generada automáticamente con confianza media Figure 2. North side of La Tembladera wetland in April 2019 Water budget The water balance of wetlands depends on interactions among inflows and outflows, showing the changes in the surface-water volume for a given period time. Hence, the basic mass balance equation, is used to express the hydrologic processes in a wetland and it is often referred to as a water budget. The water balance was estimated for two years (2018 and 2019) using the general water mass balance equation [26]: where is the volume of water storage per unit of time; P the precipitation; Qin the surface inflows from rivers, streams, marine sources, etc.; GWi the groundwater inflows; ET the evapotranspiration; Qo the surface outflows; and GWo the groundwater outflows. Concerning the surface inflows, La Tembladera wetland receives freshwater from the Santa Rosa and Arenillas rivers, which are connected with the wetland through a system of canals and gates: the Bellavista canal, San Agustín canal and the Estero Pinto [27]. Regarding the surface outflows, the wetland supplies water for agricultural purposes through several canals of irrigation, and the excess of water is drained through the Negrito and Huásimo canals [24]. The inflows data from the Bellavista canal, San Agustín canal, Estero Pinto, and the outflow data from one of the irrigation canals were taken from [24] and the average monthly values are presented in Table 1. The San Agustín and the irrigation canals have irregular flows due to the gates manipulation by the farmers [24]. The canals were considered as partially open. The outflows from the Negrito and Huásimo canals and all the irrigation canals were not included due to the lack of data. Table 1. Canals inflows and outflows Bellavista canal, m3/month San Agustín canal, m3/month Estero Pinto, m3/month Irrigation canal, m3/month Open Partially open Open Partially open 9.6×106 61.57×106 3.6×106 1.06×105 34.27×106 3.1×106 Temperature and Precipitation (P) Temperature and precipitation data from January 2018 to December 2019 were obtained from the National Institute for Meteorology and Hydrology of Ecuador (Instituto Nacional de Meteorología e Hidrología, INAMHI). These data were collected from La Cuca Meteorological station (6 km from La Tembladera wetland) and were used to estimate the potential evapotranspiration, actual evapotranspiration, runoff from rainfall and infiltration. Estimation of potential evapotranspiration (PET) The Thornthwaite method is a temperature-based method and was used for the PET calculation since depends on air temperature records that are, commonly, available data [28]: 1. To calculate Potential Evapotranspiration (PET), the Monthly Thornthwaite Heat Index (i) estimation is obtained using the following formula: where t is mean monthly temperature. 2. Annual Heat Index (I) was calculated as the sum of the Monthly Heat Indices (i): 3. Potential Evapotranspiration (PET) estimation was obtained for each month applying the equation: where PET non corrected is the monthly potential evapotranspiration, considering a month is 30 days long and there are 12 theoretical sunshine hours per day, mm/month; t is the average monthly air temperature, °C; I the Annual Heat Index; α the cubic function of I and was calculated with the following equation: α = (675 · 10-9 ·

About the authors

Priscila Jackeline Arias Ordonez

Peoples’ Friendship University of Russia (RUDN University)

Author for correspondence.
Email: arias-op@rudn.ru
ORCID iD: 0000-0003-2204-0516

PhD in Earth Sciences (Ecology), Senior lecturer, Department of Environmental Safety and Product Quality Management, Institute of Environmental Engineering

6 Miklukho-Maklaya St, Moscow, 117198, Russian Federation

Carlos Vladimir Suasnavas Lagos

Peoples’ Friendship University of Russia (RUDN University); Moscow University named after A.S. Griboedov

Email: suasnavas-lagos-k@rudn.ru
ORCID iD: 0000-0002-8799-4276

MSc, assistant, Department of Foreign Languages, Academy of Engineering, RUDN University; Lecturer, Institute of Linguistics, Moscow University named after A.S. Griboedov

6 Miklukho-Maklaya St, Moscow, 117198, Russian Federation; 21 Shosse Enthusiastov, Moscow, 111024, Russian Federation

Marianna D. Kharlamova

Peoples’ Friendship University of Russia (RUDN University)

Email: kharlamova-md@rudn.ru
ORCID iD: 0000-0002-1032-4186

PhD in Chemistry, Associate Professor, Department of Environmental Safety and Product Quality Management, Institute of Environmental Engineering

6 Miklukho-Maklaya St, Moscow, 117198, Russian Federation

Winston Rodolfo Arias Ordonez

Peoples’ Friendship University of Russia (RUDN University)

Email: 1032195477@rudn.ru
ORCID iD: 0000-0001-6832-1706

bachelor student, Institute of Environmental Engineering

6 Miklukho-Maklaya St, Moscow, 117198, Russian Federation

References