Problems related to water quality

The lack of a historical series of basic data on the physical, chemical, and biological properties of the basin’s waters makes it impossible to interpret results on the quality of the waters with any reasonable degree of accuracy and coverage. From studies conducted by the CIRA/UNAN in Lake Nicaragua in 1993 and 1994, the lake was found to have oligomesotrophic characteristics. It was found that the supply of oxygen dissolved into the lake through photosynthetic processes was very low, and that the oxygenation of a great portion of the water mass was mechanical, mainly due to the supply of atmospheric oxygen by the wind and rainfall, and by simple diffusion through the interface of water and air. Nevertheless, this study indicated that the possibility of eutrophication in areas receiving chemical and biological pollutants from discharges of municipal and industrial waste water should not be disregarded, as shown by the concentrations of phosphorous which were present at high levels of between 50 and 62 mg/l (62 and 50 m g/l in March and April 1993, respectively). Agricultural activities carried out in the drainage area of the lake were also reported to contribute to erosion,increasing turbidity and the concentration of insecticides and agrochemicals in the waters of the lake and its runoff.

From the information in Table 2 and Table 3 of, the waters of the lake were found to have the following characteristics:

• total alkalinity varied little, indicating that the waters of the lake have a good acid regulatory capacity;

• there were high levels of boron in the form of sodium and/or calcium borate;

• high levels of total coliforms and low concentrations of fecal coliforms were present, which allow the water to be used for irrigation, bathing, and recreation;

• there was a low level of chloride;

• DQO and fluoride levels were low,

• phosphorous levels were higher than those permitted for surface waters used for human consumption;

• total dissolved solids, due to discharges of urban and industrial effluents and soil erosion, were below the permissible limits for first class surface waters.

Analysis of sediment taken from Lake Nicaragua showed levels of pesticides in excess of the amounts permitted for the protection of fresh water organisms. This situation must be studied in greater depth given the impact that pesticides can have on the quality of the water in the lake and its ecosystem.

One source of pollution of Lake Nicaragua that has not been evaluated is the possible runoff from Lake Managua into Lake Nicaragua, through the Tipitapa River when the water from Lake Managua rises to 41.30 masl. During this century, this transfer has occurred on four occasions: in 1933 when it reached its highest historical level (43.44 masl), in 1955 when it reached the second highest level (42.36 masl), in 1982, and in October 1998 when, as a result of Hurricane Mitch, it rose to 42.10 masl. During the last episode, the volume of water transferred increased with the rainy season in 1999, when the waters of Lake Managua reached a height of 42.17 masl in mid-October. This extreme elevation is expected to exceed the 1955 level before the current rainy season is over, increasing the flow of water to Lake Nicaragua even further. According to the figures published by the Nicaraguan Institute of Territorial Studies, the current flow rate of the runoff is some 80 m³/sec. These flows are polluted by municipal and industrial wastewater and solid waste from Managua; by a natural salination process, which increases with the accelerated erosion in the drainage basin; and by the runoff of agricultural chemicals used in farming. In 1990, the concentration of dissolved salt was some 1,400 mg/l; in 1972 the concentration was less than 1,000 mg/l. Studies also indicate the presence of heavy metals in samples of water and in fish taken from the lake. It should be noted that a very important action in the Lake Managua sanitation program promoted by the government is the construction of a spillway to regulate the outflow of water from this lake to Lake Nicaragua and maintain the volume of Lake Managua at a prescribed level. With the building of this spillway, there would be a constant outflow of the polluted waters of Lake Managua into Lake Nicaragua through the Tipitapa River. The environmental impact of this work has not yet been evaluated.

In respect of the San Juan River, the studies carried out by CIRA/UNAN show that the turbidity of the water, which prevents the sunlight from penetrating, has inhibited the production of phytoplankton. The low levels of primary productivity and limited biomass as expressed by chlorophyll-a concentrations were observed at their lowest levels in the Sarapiquí River and at their highest levels in the San Juan River delta. The latter site had the highest total concentration of phosphorous and above-average levels of nitrate. From the information in Table 4 of Annex 3 it can be deduced that the waters of the San Juan River have the following characteristics:

• although total concentration of solids is lower than the prescribed international standard (i.e. those adopted by Brazil and Canada), the turbidity levels exceed the maximum admissible limits, mainly in the Melchora, Bartola, Zapote, Medio Queso, San Carlos, Poco Sol, and Sarapiquí rivers and in the San Juan River delta, possibly as a result of soil erosion, and the absence of protective forests in the corridors along those rivers;

• the concentrations of iron exceed the maximums recommended for human intake, the rivers on the right bank of the San Juan River being in the most critical condition;

• the high bicarbonate alkalinity, reflected by high pH and hardness values in the water, indicate a high tendency to incrustation or aggressive waters;

• the high concentration in phosphorous detected in the Sarapiquí, San Carlos and San Juan River deltas can be associated with the use of phosphates to fertilize the soil;

• no pollutants were detected in the samples of sediment from the San Juan River and its tributaries.

Erosion by water is a problem in most areas of the basin. Owing to the heavy rainfall, parts of the soil act like liquids and are lost as a resource, being transported to, and deposited in the receiving rivers, thereby diminishing the quality of the water both for consumption and for aquatic flora and fauna. Soil erosion also transports the fertilizers and pesticides used in agricultural activities and the contaminants leached from municipal and industrial solid wastes, which are usually deposited in open dumps within settlements and in the industrial zones located in the SJRB. The final disposal and proper management of wastes is a problem in most of the urban centers in the SJRB. Few centers have adequate disposal facilities for solid wastes, although Ciudad Quesada, the largest urban center on the Costa Rican side of the SJRB, does have a sanitary fill. Technical studies on pollution, particularly on leachates which could have a negative effect on the environment and on surface and ground waters, are lacking. In Nicaragua, the towns located in the basin that produce the largest volumes of solid waste are Granada, Masaya, Rivas, Boaco, Juigalpa and San Carlos. In the small towns, the garbage collection system is deficient and trash is usually dumped in open areas. It is rarely removed or covered, resulting in putrid odors and a proliferation of flies and other problems. Only 32% of the population in the basin has a solid waste collection system. The majority of the scattered, rural population mostly digs pits for its solid waste. In most cases, when the pits fill up, they are set alight or sometimes covered and new ones dug to dump more trash. In some cases, the solid waste is dumped directly on the ground or in riverbeds and gullies. There is generally little awareness or education about solid waste disposal; everywhere trash can be found on the ground, on the roads, and in rivers. In the larger centers in the Nicaraguan sector of the basin, garbage collection systems cover about 45% of the population. In all cases, the solid waste collected is dumped in open areas. There are very few towns in which solid waste is used to produce organic fertilizer.

The excessive use of pesticides is a general problem in most agricultural activities. With the exception of subsistence agriculture, agricultural chemicals are widely used. In the project area, 92% of the farmers are small farmers. Subsistence agriculture represents only 6.5% of the surface area and does not use significant quantities of agricultural chemicals for economic reasons. Likewise, the excessive use of fertilizers can have negative effects on both surface and ground water sources. As a result of the deposition of nitrogenous fertilizers in water bodies, the aquatic flora multiplies causing ecological imbalances with negative consequences (including high consumption of oxygen as the organisms die and decompose) within the aquatic ecosystem. This problem is caused in part by the exhaustion of the natural fertility of the soil and its continued use, requiring the artificial supply of the nutrients necessary for normal crop development. Due to the fact that the regulations related to the use of pesticides and fertilizers are very weak or nonexistent, these agrochemicals are used irrationally, far in excess of the real demands of cultivation, with inefficient application and poor handling. This affects the biota in general, polluting the surface and ground waters, and creating occupational health problems. On the other hand, there are crops in the basin area that require high agrochemical use, such as bananas, vegetables, root crops, and sugar cane. Table 5 of Annex 3 shows the main crops produced in the SJRB and the most widely used chemicals. The geographic areas where this situation occurs are mostly the wetlands, Malacatoya, Medio Queso, Guacalillo, Ochomogo, Palo Ralos, Río Zapote, where banana plants (Pococí), citrus (San Carlos CR) and sugar cane, common to a number of localities in the basin, are grown.

Industrial wastewater has traditionally been a problem both in Nicaragua and in Costa Rica. The lack of norms to regulate effluents from industries and institutional weaknesses (technical and financial) have severely limited the ability to oblige industries to treat their wastewater. In many cases, because there are no controls on these waters, companies do not use treatment techniques that would raise production and operating costs. Businessmen view this measure as an expense and not as a requirement for sustainable development. Given the range of industrial operations in the basin, the composition of wastewaters may vary considerably depending on the type of industry. In most industries, these waters have been diverted to the rivers and streams to save economic resources. The critical points where the problem of pollution with industrial waste water arises are in the capitals of cantons and major municipalities, where industries are established, the banana-growing areas, fishing zones, sugar plantations, coffee plantations, and citrus and dairy processing plants.

In Costa Rica, attempts have been made to control this situation. Coffee plantations, for example, have made strides in the treatment of their wastewater with oxidation lagoons. Cane plantations, slaughterhouses, pig farms, and other businesses are doing the same. The discharge from these companies is analyzed by the Ministry of Health, which establishes ranges for different substances and compounds, though it faces serious restrictions in terms of controlling effluents. The Ministry of Environment and Energy, MINAE, is responsible for the administration of water resources within the entire national territory of Costa Rica, through. the Department of Waters located at the National Meteorological Institute.

In Nicaragua, MARENA is responsible for controlling pollution through the General Directorate of Environmental Quality. The Ministry of Health and the INAA focus on the quality of the water supply for human consumption. The CIRA is a specialized center of the Universidad Nacional Autónoma de Nicaragua (UNAN), which has laboratories for various analyses of water quality. There is a National Water Resource Commission to coordinate these activities.

The most densely populated towns in the SJRB are Masaya, Granada, Boaco, Juigalpa and San Carlos. Ciudad Quesada is the largest urban area on the Costa Rican side. The Nicaraguan urban population in the basin makes up 45% of the total (354,834 inhabitants), while on the Costa Rican side, the urban population amounts to 32% (91,530 inhabitants) of the total. As a result, both rural and urban wastewater volumes are significant, resulting in a high pollution potential; the same can be said for human excrement. The major urban centers have sewage treatment systems. Most of the rural population lacks the minimal basic sanitation services and conditions. The problem of wastewater is accentuated due to the unplanned spread of human settlements, which have no basic services whatsoever and so increase the stress on the existing ones. An analysis conducted by the WHO (World Health Organization) concludes that the Nicaraguan sector of the basin, because of its denser population, can potentially generate some 3.5 to 7.7 times more municipal wastewater pollution than the Costa Rican sector of the basin. Table 6 of Annex 3 estimates the pollution potential of the human settlements based in the basin.

Actions to help improve the quality of surface and ground waters include the promotion of programs on soil conservation, integrated pest management, construction of proper sanitary fills, and treatment of municipal and industrial wastewater. It will also be necessary to develop technical assistance programs for the management and use of agricultural chemicals and their dangers to health and the environment. Other actions include technical assistance, refraining from the use of fertilizers in zones near rivers, reforestation or regeneration of the natural vegetation on river banks, reduction in the dosage of fertilizers or their application in smaller doses, covering the fertilizer to prevent it from being washed away by rain, and establishing environmental education programs indicating the negative effects of fertilizers on the environment and aquatic ecosystems, both fresh water and marine. It is necessary to develop systematic programs to monitor the quality of water in order to verify the progress made in controlling the pollution of water bodies. In addition, research programs are required to better ascertain the dynamics of erosion, sedimentation, and pollution and so provide guidelines for their control. Other actions that will help mitigate and control this problem are the development of plans and strategies for integrated management of water resources and other natural resources.

© 2004 PROCUENCA-San Juan   -   Terms of Use and Policy Notice