Egu Cuban Karst Aquifers

Managing environmental problems in Cuban karst aquifers L.F. Molerio León CESIGMA, S.A., P.O. Box 6219, CP 10600, Habana 6, Ciudad de La Habana, Cuba Email: [email protected]

M. Parise

NH8.03. Natural and anthropogenic hazards in karst areas EGU2007-A-01839

National Research Council, IRPI, Bari, Italy Gruppo Puglia Grotte, Castellana-Grotte (BA), Italy Email: [email protected]

Abstract. Cuban karst covers almost 66% of the territory. The most important aquifers are of karstic nature and comprise 80% of the country’s groundwater resources. These aquifers are mainly unconfined and built by Miocenic carbonate rocks morphologically expressed as very gentle coastal flatlands. Only a small part of the total karst, almost 7 500 km2 is occupied by low to medium height mountains of Jurassic to Paleogene rocks.The enlarged configuration of the country produces two main slopes, at north and south, of the central water divide. river basins are small and bigger catchments are only found in the scarce rivers running eastward or westward. Flashfloods characterizes the response to the heavy rains associated with the extreme events typical of the humid tropics. Cuba is also an archipelago. Close to 4000 small and very small islands (named “cayos”) surrounds the two main islands: Cuba and the Isle of Youth. Economy is mainly agriculturally based as most of the Caribbean, while other activities are rising in importance as mining, light industry and tourism. A phenomenon of high concentration of the population in the capital of the country or in the main cities has developed since the 1960´s and only stopped and slightly reverted locally in the last five years. Therefore, the geological, geographical and economic framework of the country defines the environmental problems that should be managed for an adequate protection of groundwater quality. This paper offers an overview of the main pollution sources of the country and how risk assessment is developed in the particular case of a karst territory in the humid tropics.

INTRODUCTION Cuban karst covers almost 66% of the territory (Fig. 1). The most important aquifers are of karstic nature and comprise 80% of the country’s groundwater resources. These aquifers are mainly unconfined and built by Miocenic carbonate rocks morphologically expressed as very gentle coastal flatlands. Only a small part of the total karst, almost 7 500 km2 is occupied by low to medium height mountains of Jurassic to Paleogene rocks (Fig. 2). While in the flatlands conduit and diffuse flows are observed, dominating the latter, in the mountains, conduit flows dominates. Because of the enlarged configuration of the country two main slopes, at north and south, are founded after the central water divide. Thus, river basins are small and bigger catchments are only found in the scarce rivers running eastward or westward. Therefore, flashfloods characterizes the response to the heavy rains associated with the extreme events typical of the humid tropics. Cuba is also an archipelago. Close to 3 500 small and very small islands (named “cayos”) surrounds the two main islands: Cuba and the Isle of Youth.

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Fig. 1. Cuban karst areas (generalized by H. Farfán)

Fig. 2. Cuban flatlands commonly articulate without transition with the mountainous landscape (Photo by L. Molerio).

Economy is mainly agriculturally based as most of the Caribbean, while other activities are rising in importance as oil exploration and production, mining, light industry and tourism. A phenomenon of

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high concentration of the population in the capital of the country or in the main cities has developed since the 1960´s and only stopped and slightly reverted locally in the last five years. Therefore, the geological, geographical and economic framework of the country defines the environmental problems that should be managed for an adequate protection of groundwater quality. This paper offers an overview of the main pollution sources of the country and how risk assessment is developed in the particular case of a karst territory in the humid tropics. VULNERABILITY OF KARST AQUIFERS Vulnerability of aquifers depends on several factors linked with the geological structure, climatic conditions, land and water use and economic framework. Karst aquifers are often more complicated in defining vulnerability because of the heterogeneity and anisotropy of the water bearing strata, the close relationship between landforms and drainage and the degree of hydrological activity of the karst system (Molerio, 2004). Molerio (2004) has identified a general chart of karst aquifer vulnerability and Gutiérrez & Molerio (1996) and Molerio & Gutiérrez (1999) have considered, in detail, the factors controlling aquifer vulnerability in the case of nitrification processes in Cuban karst aquifers. Excluding components considered by them specifically attaining the agricultural framework, the general picture is resembled in Table 1 and, generally speaking has been found useful in the assessment of vulnerability of karstic aquifers. Foster & Hirata (1988) defined vulnerability as a function of the properties of the unsaturated zone. If these properties in karst systems are properly defined, no conceptual modifications need to be made to the criteria of these authors. Karst systems are characterized by the following properties (Molerio, 1985, 1992): • Thermodynamically, karst is an open system interacting with the surrounding media. • Variables describing system's physical properties shows a progressive three-dimensional anisotropy. • For any kind of basic measure of a characteristic length (area, volume, length, effective diameter) the karstic space is rigorously hierarchisized. • Four types of constitutive spaces are then developed, generically designed -in decreasing order of characteristic length- as caves, joints, pores and solid matrix. • Each of the constitutive spaces exhibits their own flow domain and, among them, an active exchange of mass, moment and energy take place. • According to this the physical properties field is structured and defined for each space. • Responses to external or internal -natural or artificial- inputs of mass, energy and moment are hierarchically modulated by the system's internal structure and capability to assimilate stresses. • The scale factor exerts a strong influence on the physical meaning and stochastic behavior of the physical properties .Within the system, work development produces self-regulated energy dissipation structures feeding back the whole set of processes. • Thus, the system and in particular, the physical properties defining it are highly time-dependent at different space and time scales. • The karstification process is irreversible; its evolution is unidirectional towards increasing levels of entropy. In fact those properties mean that anisotropy and heterogeneity are due to the differentiated development of karstification in carbonate rocks. Morphological features are developed selectively. Therefore they behave also different with respect to vertical or horizontal flows (Fig. 3).

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Dolines and vertical shafts or horizontal and also subhorizontal caves absorbing overland or streamflow are the carriers of great water volumes entering fast to the aquifer system. Responses to these concentrated inputs use to be more or less rapid, depending on the initial state of the system and its inertial properties. Commonly, when connected to water table aquifers, response tends to be fast, seeming a piston-flow behavior that is a very useful pattern to explain and mathematically describe aquifer hydrodynamics. Less developed karst features, clay-filled vertical caves, joints and fissures, behave more slowly to inputs, delaying flow to the saturated zone and, in turn, producing a second peak in groundwater levels or at least a delayed response to mass transfer. These two extreme behaviors produce a complex interaction and behavior of the system with respect to mass transport processes. While physical properties are different for each of the involved spaces, time responses are also different. The so-called multiphase flow is most commonly observed in karstic systems than anywhere. An intensive karst development in this unsaturated zone allows for two main infiltrating paths to ground waters. Therefore, • A fast concentrated recharge takes place along vertical groundwater-connected shafts or following horizontal or subhorizontal caves. Surface flow to those karst features occurs in two main ways: a diffuse overland flow and a concentrated or channeled flow following streams entering caves. • A slow, diffuse recharge takes place following pores, joints and fissures less karstified. Both mechanisms are also important to explain pollution hydrodynamics in karst terrains. Different concentrations, flow paths and arrival times are controlled by the recharge system. Mathematical modeling or analytical solutions has also to account whether or not contamination sources are punctual or diffuse inputs. While one group of boundary conditions concerning infiltration capability depends on the differentiated karst development, the other group depends upon the anthropogenic effects over karst. Therefore, karst land and water use strongly influences system’s vulnerability. According to this, aquifer vulnerability to nitrification processes depends on the interaction of the factors described in Table 1. Six major pollution sources to ground waters are identified in Cuba: • Sea water intrusion • Agriculture and Husbandry • Domestic wastes • Industry • Mining (including oil exploration and production)

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Fig. 3. Idealized sketch of a karstic system showing extreme features for infiltrating waters (modified and adapted from Mangin, 1975)

Sea water intrusion The most important aquifers are located beneath the southern coast of Cuba. Sea water intrusion, therefore, becomes the most common and extensive source affecting water quality. In the small and very small islands it is also the main factor affecting groundwater quality (Fig. 4). Fig. 4. The main island of Cuba has almost 3600 km of coastline vulnerable to sea water intrusion (Photo by L. Molerio). .

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Karst exerts a differentiated influence upon distribution and intensity of sea water intrusion. Flooded karst conduits shows differentiated vertical saline distribution depending on caves depth below sea level disregarding the distance with respect to the shoreline. While depth of flooded caves is associated with the development of ancient sea level positions, cave level distribution is a controlling factor of present sea water intrusion. In several cases, isolated lens of intruded sea water are found dozens of kilometers inland. In conduit-flow aquifers, sea water intrusion is controlled by the amount of water discharged by submarine or shoreline springs. Commonly, under the same abstraction regime, rainfall distribution and land-use patterns diffuse - flow aquifers are more intruded than conduit-flow systems. Whereas both types of aquifers coexist in Cuban karst, is not uncommon to observe an irregular pattern of horizontal and vertical distribution of sea water intrusion depending on the above mentioned factors. Agriculture Agricultural impact on groundwater is due to several factors as land-use pattern and irrigation, culture and husbandry practices and on soil cover properties. The most important evidences of agricultural contamination of ground waters are the presence of nitrates and pesticides in ground waters (Fig. 5). Fig. 5. The terra rossa deposits are the most important spoils in Cuban karst (Photo by L. Molerio).

Since the 1960´s irrigation and fertilization practices developed fast in Cuba. Nitrate concentration in ground waters increased suddenly from a background level of 0 to 10 mg/l to values over the permissible limits of drinking water in several basins. Fertilization was the main responsible for this situation and gross estimates accounts for input values between 80 and 120 kg N/Ha/y. Nitrate groundwater contamination in Cuba is always related with its agricultural economic framework. Evidences of an increase in nitrate concentrations are observed in monitoring wells in the

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last decades. The karst nature of Cuban territory and of its main aquifers allows an average high vulnerability to nitrate pollution. As a matter of fact, the knowledge of the factor involved in leaching process allowed an achievement of the ranks of nitrogen supply to ground waters, that could be estimated between 40-80 kg N/Ha/y. Local variability are related with the type of water used for irrigation, the kind of crops and the nitrate concentration of irrigation waters. The application of a simple mixing-cell model allowed to account N supply from the unsaturated zone, effective recharge, annual variation of natural and induced recharge, the involved volume with respect to the effective depth considered and the nitrogen base level of the aquifer, allowed to compute and validate a methodology described in a recent paper. In Cuba, were high level nitrate ground waters are used for irrigation purposes it becomes evident that the nitrogen loads supplied from irrigation is relevant for computations and must be included in any mathematical model. Values as high as 30 kg N/Ha/y has also to be considered in fertilization balances. Once started the nitrification process, concentrations will tend to fluctuate around the computed concentration because of the inter annual behavior of rainfall and of the effective recharge, associated with local intense precipitation or large droughts typical of tropical climates. Recovery processes are slow and under Cuban conditions, could reduce between 10-15% nitrate concentrations in about 10 years, figures that are much lower than the estimates for other climates or type of aquifers. Domestic wastes Direct infiltration of crude or poorly treated domestic wastes (Fig. 6) is important sources of groundwater pollution, together with the point sources of septic tanks and latrines. Discharges from oxidizing ponds and failures in depuration processes are the main cause of direct contamination of ground waters not only in karst but in all Cuban aquifers. Sewerage services extend to 39% of the population. Table 2 shows the distribution of sanitation services in Cuba in 1993. Industry Industrial wastes are one of the most extended pollution sources. Particularly hazardous is the contamination derived from the sugar cane industry, promoting sacarose enriched, low pH and high temperature waters whose impact on groundwater quality is traduced in lowering COD, SO4 bacteria and indirectly, also in local subsidence due to CO2 enriched waters accelerating limestone dissolution. Pollution endangering from the light industry comes from textile factories and paper mills. Colored waters from textile factories have been used for a long time as tracers in western Cuba. Another source of pollution comes from the pharmaceutical and chemical industry, but because of being recent developed industries are much better controlled by the environmental agencies.

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Fig. 6. Untreated sewage waters are a common threat to groundwater in urban karst lands (Photo by L. Molerio).

Fig. 7. Sugar factories are one of the most important sources of groundwater pollution of karst waters in Cuba (Photo Cuban Environmental Agency).

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Table 2. Sanitation services in Cuba, (Figures in millions of inhabitants) Total population

% of population with sanitation services Appropriate service

Sector

Inhabitants

%

Sewerage

Urban Rural Total

8.27 2.65 10.92

75.7 24.3 100.0

35.0 52.0 39.0

Tanks and Total latrines

31.6 46.8 35.2

66.6 52.0 74.2

Inadequat Total e with solutions service

30.0 20.0 27.6

96.6 72.0 90.6

Populat ion without service % 3.4 28.0 9.4

Mining Accelerated mining development carried out several problems of surface water pollution instead of groundwater contamination because nickel, copper, iron and gold mining are related with nonkarstic rocks (Fig. 8). Their effect on groundwater is less dangerous because the relative isolation of these mines with respect to carbonate terrains. Oil well drilling and oil fields are, up to now, the most dangerous sources of groundwater pollution derived from mining (Fig. 9). The most important oil fields have been developed over limestone aquifers increasing the risk of environmental problems in the country. Fig. 8. Open pit mining threatens groundwater quality and quantity because direct pollution and evaporation (Photo by L. Molerio).

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Fig. 9. Oil well drilling and oil fields are, up to now, the most dangerous sources of groundwater pollution derived from mining (Photo by L. Molerio).

RISK ASSESSMENT Risk assessment of groundwater pollution is institutionally based by: • a legislative framework • a monitoring network of groundwater quality and the corresponding data processing and alarm systems • a contingency plan for environmental emergency Legislative framework Laws dealing with inland waters, soils and environmental management and protection have been systematically improved since the 1960´s. The Constitution of the Republic of Cuba considers environmental protection as a right and a duty of the State and of the citizens. In what concerns to groundwater protection, the responsibility lies in the National Institute of Water Resources being the Center of Hydrology and Water Quality (CENHICA) the national agency in charge of monitoring and implementation of water resources protection. Monitoring Network and Data Processing and Warning System The national ground and surface monitoring network in operation is administrated by the CENHICA-INRH since the second half of 1960´s except for rainfall and several hydrometric stations in operation, some of them since the beginning of the 20th century. Table 3 shows the structure of the monitoring network.

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Table 3. Monitoring network of the Republic of Cuba (after Molerio et al.,1998) 1. Surface waters.

Measured variable: Rain

Stations Rain gauges Rain gauges recorders Surface flow Hydrometric Evaporation, relative humidity, Climatic (mainly evaporimetric wind, insolation stations) Water quality

Total 1997 1083 50 75 768

2. Groundwaters

Measured variable: Groundwater level Groundwater salinity Groundwater quality

Stations Observation wells Observation wells Observation wells

Total 2399 290 1354

Warning systems are integrated by selected stations monitored on a daily, weekly or monthly basis. Variables measured are evaluated in terms of their variations in water quality or resources. Simulation models have been implemented in several basins or aquifer systems in order to diagnose and forecast its behavior. The structure of this informative network is depicted in table 4. Table 4. Warning systems for environmental emergency of inland waters. 1. Surface waters.

Measured variable: Rain Water quality

Stations Rain gauges

Total 696 Variable. Depending on the season, population supplied and monitoring programme

Stations Observation wells Observation wells

Total 527 Variable. Depending on the season, population supplied and monitoring programme

2. Groundwaters

Measured variable: Groundwater level Groundwater quality

FINAL REMARKS The geological, geographical and economic framework of the country defines the environmental problems that should be managed for an adequate protection of groundwater quality. Vulnerability of Cuban aquifers depends on several factors linked with the geological structure, climatic conditions, land and water use and economic framework of the country. Karstic aquifers, extended over 65% of the national territory, are often more complicated in defining vulnerability

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because of the heterogeneity and anisotropy of the water bearing strata, the close relationship between landforms and drainage and the degree of hydrological activity of the karstic system. Five major pollution sources to groundwater identified in Cuba are: sea water intrusion, agriculture and husbandry, domestic wastes, industry and mining. Groundwater quality is then managed by a Warning System integrated by selected stations monitored on a daily, weekly or monthly basis. Variables measured are evaluated in terms of their variations in water quality or resources. Simulation models have been implemented in several basins or aquifer systems in order to diagnose and forecast its behavior. REFERENCES Foster, S.S.D. and Hirata, R (1988). Groundwater pollution risk assessment a methodology using available data. Pan American Center for Sanitary Engineering and Environmental Science (CEPIS), Lima, Perú Gutiérrez J. and L.F. Molerio (1996): Nitrates In Cuban Groundwaters. in/ L. Candela (Edit): Agricultural Threats to Groundwater Quality. Mangin, A. (1975): Contribution a létude hydrodynamique des aquifers karstiques. Thése. CNRS: Moulis: 356p Molerio León, Leslie F. (1975): Esquema Geoespeleológico Preliminar de cuba (Memoria Explicativa del Mapa de las Regiones Cársicas de Cuba a escala 1:1 000 000). Simp. XXXV Aniv. Soc. Espel. Cuba, La Habana, :68 Molerio León, Leslie F. (1985): Dominios de Flujo y Jerarquización del Espacio en Acuíferos Cársicos. Simp. XLV Aniv.Soc. Espel. Cuba, La Habana,: 54 Molerio León, Leslie F. (1992): Complementos de un Modelo de Simulación Matemática del Desarrollo del Carso. GTICEK. Taller Internac. sobre Cuencas Experimentales en el Karst, Matanzas, Publ. Universitat Jaume I de Castelló,:83-92 Molerio León, L.F. & J. Gutiérrez Díaz (1999): Agricultural Impacts on Cuban Karstic Aquifers in/ Drew, D.& H. Hötzl [Eds.] (1999): Karst Hydrogeology and Human Activities, A.A. Balkema, Rotterdam,:76-78 Molerio León, L.F., O. Barros, N. Gómez, J.L. Gelabert (1998): Cuba. Red Nacional de Monitoreo del Régimen de las Aguas Subterráneas. Red Internac. de Organismos de Cuenca. Carta de la Red. (6), 1er trimestre, :9 http://www.inbo-news.org/pdf/inbo6.pdf

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