Ten years of limnological monitoring of a modified natural lake in the tropics: Cote Lake, Costa Rica.

It is located 650m above sea level along the boundary between the North Caribbean and Pacific slopes, near the Southern end of the volcanic Guanacaste mountain range. In the early 1980s the lake's main outlet was dammed and the outflow was diverted into Arenal Reservoir. Lake Cote was first studied in 1990-1991, and later in 2001, before it was again modified by raising its dam by one meter to use its outflow for hydroelectricity. From 2002 to 2010 it has been monitored twice a year for changes in its limnology. Here I present a summary of its basic characteristics and an analysis of their changes through time. The lake is discontinuous polymictic, and sometimes develops a thermocline at 6m depth that may last for several days as evidenced by the occasional development of an anoxic layer close to the bottom. Since its modification for hydropower production, the surface water temperature has attained higher values than before. Oxygen levels in the lake show periods of hypoxia to anoxia in the hypolimnion, that have become more frequent since modification. Despite its turbid water, the lake has low levels of nutrient concentrations and of chlorophyll a. The trend in these parameters in recent times is a reduction in chlorophyll a and an increase in water transparency, implying a reduction in primary productivity. These changes are discussed in relationship with anthropogenic factors such as the modification of the lake and its management, changes in landscape around the lake and global climate change.

Ten years of limnological monitoring of a modified natural lake in the tropics: Cote Lake, Costa Rica / Diez años de monitoreo limnológico de un lago natural modificado en los trópicos: el lago Cote, Costa Rica

It is located 650m above sea level along the boundary between the North Caribbean and Pacific slopes, near the Southern end of the volcanic Guanacaste mountain range. In the early 1980s the lake’s main outlet was dammed and the outflow was diverted into Arenal Reservoir. Lake Cote was first studied in 1990-1991, and later in 2001, before it was again modified by raising its dam by one meter to use its outflow for hydroelectricity. From 2002 to 2010 it has been monitored twice a year for changes in its limnology. Here I present a summary of its basic characteristics and an analysis of their changes through time. The lake is discontinuous polymictic, and sometimes develops a thermocline at 6m depth that may last for several days as evidenced by the occasional development of an anoxic layer close to the bottom. Since its modification for hydropower production, the surface water temperature has attained higher values than before. Oxygen levels in the lake show periods of hypoxia to anoxia in the hypolimnion, that have become more frequent since modification. Despite its turbid water, the lake has low levels of nutrient concentrations and of chlorophyll a. The trend in these parameters in recent times is a reduction in chlorophyll a and an increase in water transparency, implying a reduction in primary productivity. These changes are discussed in relationship with anthropogenic factors such as the modification of the lake and its management, changes in landscape around the lake and global climate change. Rev. Biol. Trop. 62 (2): 567-578. Epub 2014 June 01.

Esta localizado a 650m sobre el nivel del mar en el límite entre las llanuras del Norte y la vertiente del Pacífico en la Cordillera de Guanacaste, Costa Rica. Al inicio de la década de 1980 se construyó una represa en el río de desagüe y el caudal de salida fue desviado hacia el Embalse Arenal. Se realizó un primer estudio entre 1990 y 1991, y luego en el año 2001 antes de que se construyera una nueva modificación del lago mediante el levantamiento del nivel de la presa en un metro con el fin de utilizar la descarga para la producción de energía hidroeléctrica. Del 2002 al 2010 se realizó un monitoreo limnológico dos veces al año. Aquí se presenta un análisis de las principales características y de los cambios a través del tiempo. El lago es polimíctico discontinuo y desarrolla una termoclina intermitente a 6m de profundidad, la cual puede perdurar por varios días o semanas a juzgar por el desarrollo de una capa anóxica cercana al fondo. Desde su modificación la temperatura superficial del lago ha alcanzado valores mayores a los reportados con anterioridad. El hipolimnion muestra periodos de hipoxia a anoxia que se han vuelto más frecuentes. A pesar de la turbidez del lago, la concentración de nutrientes y de clorofila a son bajos. La tendencia en tiempos recientes es a una reducción de la clorofila a y un aumento en la trasparencia del agua. Estos cambios son similares a los observados en lagos donde se ha logrado atribuirlos al cambio climático global. También se pueden deber a la modificación del flujo del efluente por la operación intermitente de la planta hidroeléctrica, que favorece la acumulación de calor en la columna de agua. Esto debido a que otros factores, como el cambio en el uso del suelo en los alrededores del lago ocurrieron en la década de 1980, por lo que no se les puede atribuir una influencia en los cambios observados en los últimos 10 años.

[Freshwater macroinvertebrates from Cocos Island, Costa Rica: species and comparison with other islands of the Eastern Tropical Pacific]. / Macroinvertebrados dulceacuícolas de la Isla del Coco, Costa Rica: especies y comparación con otras islas del Pacifico Tropical Oriental.

Freshwater macroinvertebrates from Cocos Island, Costa Rica: species and comparison with other islands of the Eastern Tropical Pacific. Cocos Island is an oceanic island in the Eastern Pacific, at 496km from Cabo Blanco, Costa Rica. This 24 km2 island is surrounded by a protected marine area of 9640 km2. it was declared National Park in 1978 and a World Heritage by UNESCO in 1997. Freshwater macroinvertebrate fauna was collected in 20 sites covering three rivers (Genio, Chatam and Sucio) and two creeks (Minuto and an unnamed creek behind the park rangers' house). Tank bromeliads or phytotelmata were also examined for aquatic macroinvertebrates. Physicochemical parameters were determined in 13 study sites. Additionally, a comparison with other islands in the Eastern Tropical Pacific was conducted to determine the most important factors controlling the diversity in Tropical Pacific islands. A total of 455 individuals were collected belonging to 20 taxa (mostly identified to genus level) from 15 families of aquatic insects. Other macroinvertebrates such as Palaemonid shrimps, Hidrachnida and Oligochaeta were also collected. The family Staphylinidae (Coleoptera) was the most abundant, followed by Chironomidae (Diptera). Diptera was the order of insects with the highest taxonomic richness. A relationship between distance and the number of families was observed supporting the premises of the Theory of island Biogeography. This relationship was improved by correcting area by island elevation, indicating that mountainous islands had the richest faunas, potentially due to high cloud interception that feeds freshwater environments favoring the establishment of aquatic fauna. Physicochemical variables were similar in all sites, possibly due to the geology and the absence of significant sources of pollution on the island.

Macroinvertebrados dulceacuícolas de la Isla del Coco, Costa Rica: especies y comparación con otras islas del Pacífico Tropical Oriental / Freshwater macroinvertebrates from Cocos Island, Costa Rica: species and comparison with other islands of the Eastern Tropical Pacific

Cocos Island is an oceanic island in the Eastern Pacific, at 496km from Cabo Blanco, Costa Rica. This 24km² island is surrounded by a protected marine area of 9 640km². It was declared National Park in 1978 and a World Heritage by UNESCO in 1997. Freshwater macroinvertebrate fauna was collected in 20 sites covering three rivers (Genio, Chatam and Sucio) and two creeks (Minuto and an unnamed creek behind the park rangers’ house). Tank bromeliads or phytotelmata were also examined for aquatic macroinvertebrates. Physicochemical parameters were determined in 13 study sites. Additionally, a comparison with other islands in the Eastern Tropical Pacific was conducted to determine the most important factors controlling the diversity in Tropical Pacific islands. A total of 455 individuals were collected belonging to 20 taxa (mostly identified to genus level) from 15 families of aquatic insects. Other macroinvertebrates such as Palaemonid shrimps, Hidrachnida and Oligochaeta were also collected. The family Staphylinidae (Coleoptera) was the most abundant, followed by Chironomidae (Diptera). Diptera was the order of insects with the highest taxonomic richness. A relationship between distance and the number of families was observed supporting the premises of the Theory of island Biogeography. This relationship was improved by correcting area by island elevation, indicating that mountainous islands had the richest faunas, potentially due to high cloud interception that feeds freshwater environments favoring the establishment of aquatic fauna. Physicochemical variables were similar in all sites, possibly due to the geology and the absence of significant sources of pollution on the island.

La Isla del Coco es una isla oceánica localizada en el Pacífico Tropical Oriental a unos 492km de Cabo Blanco. La isla cuenta con un área terrestre de 24km² y un área marina protegida de 9 640km². Fue declarada Parque Nacional en 1978 y Patrimonio de la Humanidad por la UNESCO en 1997. Se realizó una gira de recolecta del 22 de mayo al 12 junio 2008. Se recolectaron macroinvertebrados acuáticos en 20 tramos de tres ríos (Genio, Chatham y Sucio) y dos quebradas (Minuto y quebrada sin nombre atrás de estación de guarda parques). En 13 sitios se toma- ron parámetros fisicoquímicos. En total se recolectaron 455 individuos de 20 táxones de 15 familias de insectos acuáticos y otros macroinvertebrados. La familia Staphylinidae presentó la mayor abundancia seguida por Chironomidae, los dípteros fueron el orden con mayor riqueza taxonómica. Una relación entre distancia y número de familias se observó apoyando en parte la Teoría de Biogeografía de Islas. La relación mejoró al corregir área con elevación, indicando que islas montañosas tenían alta riqueza, posiblemente debido a la mayor intercepción de nubes que alimentan los ambientes dulceacuícolas que favorecen el establecimiento de la fauna acuática. Las variables ambientales fueron similares en todos los sitios.

Reconnaissance of selected PPCP compounds in Costa Rican surface waters.

Eighty-six water samples were collected in early 2009 from Costa Rican surface water and coastal locations for the analysis of 34 pharmaceutical and personal care product compounds (PPCPs). Sampling sites included areas receiving treated and untreated wastewaters, and urban and rural runoff. PPCPs were analyzed using a combination of solid phase extraction and liquid chromatography tandem mass spectrometry. The five most frequently detected compounds were doxycycline (77%), sulfadimethoxine (43%), salicylic acid (41%), triclosan (34%) and caffeine (29%). Caffeine had the maximum concentration of 1.1 mg L(-1), possibly due to coffee bean production facilities upstream. Other compounds found in high concentrations include: doxycycline (74 µg L(-1)), ibuprofen (37 µg L(-1)), gemfibrozil (17 µg L(-1)), acetominophen (13 µg L(-1)) and ketoprofen (10 µg L(-1)). The wastewater effluent collected from an oxidation pond had similar detection and concentrations of compounds compared to other studies reported in the literature. Waters receiving runoff from a nearby hospital showed higher concentrations than other areas for many PPCPs. Both caffeine and carbamazepine were found in low frequency compared to other studies, likely due to enhanced degradation and low usage, respectively. Overall concentrations of PPCPs in surface waters of Costa Rica are inline with currently reported occurrence data from around the world, with the exception of doxycycline.

Basic limnology of fifty-one lakes in Costa Rica.

We visited 51 lakes in Costa Rica as part of a broad-based survey to document their physical and chemical characteristics and how these relate to the mode of formation and geographical distribution of the lakes. The four oxbow lakes were low in elevation and tended to be turbid, high in conductivity and CO2, but low in dissolved O2; one of these, L. Gandoca, had a hypolimnion essentially composed of sea water. These were similar to the four wetland lakes, but the latter instead had low conductivities and pH, and turbidity was often due to tannins rather than suspended sediments. The thirteen artificial lakes formed a very heterogenous group, whose features varied depending on local factors. The thirteen lakes dammed by landslides, lava flows, or lahars occurred in areas with steep slopes, and were more likely to be stratified than most other types of lakes. The eight lakes that occupy volcanic craters tended to be deep, stratified, clear, and cool; two of these, L. Hule and L. Río Cuarto, appeared to be oligomictic (tending toward meromictic). The nine glacial lakes, all located above 3440 m elevation near Cerro Chirripó, were clear, cold, dilute, and are probably polymictic. Cluster analysis resulted in three significant groups of lakes. Cluster 1 included four calcium-rich lakes (average 48 mg l-1), Cluster 2 included fourteen lakes with more Si than Ca+2 and higher Cl- than the other clusters, and Cluster 3 included the remaining thirty-three lakes that were generally less concentrated. Each cluster included lakes of various origins located in different geographical regions; these data indicate that, apart from the high-altitude glacial lakes and lakes in the Miravalles area, similarity in lake chemistry is independent of lake distribution.