Water Quality at the Cárdenas-Comalcalco Basin, México

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16
In order to save space and for ease of handling, the information in the following tables 17 shows only the average and median values obtained in analyses.

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A variation was observed in water quality over the various sampling seasons in several of 20 study sites (Table 1). In most of the sampled wells nitrates levels were above 10 mg/L as

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Nitrates are the main pollutant of underground water in rural areas, especially in those 28 areas dedicated to intensive cattle raising. High levels of nitrates in the water (greater than 29 10 mg/L) have been known to cause methemoglobinemia known as blue baby illness.

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Although nitrates levels that affect small children usually do not affect older children and

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There is no a simple way to eliminate nitrates from water since it can not be evaporated with    Although there were no significant differences related with turbidity between the different 1 towns and season of year, In the rainy season only four wells were within the guidelines established in the standard at 9 the two sampling depths. While in the norte season, that increased to 5, the number of wells 10 with acceptable turbidity, in general, values increased in this season. Only the well Z5-03 11 located in Zona Verde was within the quality standard in all three seasons.

12
In the dry season, the median was of 1.55 NTU which is very below the limit of permissible 13 turbidity. However in the wells located in the village Carlos Green (Z-6) and Cañales (Z-9)

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were found to have extremely high values, 27.8 and 14.6 NTU, respectively.

15
In rainy season, turbidity was greater, with an average value of 11.78 NTU. The median was 16 set in 5.55, both values surpassed the permissible limit; in this season only water of wells

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and Cañales (Z-9) fulfilled the standards of quality over the two sampling depths. high turbidity values found are of great concern, since consumption of very muddy waters 3 constitutes a risk factor for human health, since the mud can protect to pathogen organisms 4 of disinfectants effects, besides stimulate bacterial growth and increase chlorine demand.

5
Due to the absorption capacity of some particles, they can have present harmful organic 6 compounds which should not be present in water designated for human consumption (Safe 7 Drinking Water, 1980).

8
There were not found reference values for OD in the consulted standards and references, 9 because concentrations up to saturation point in water have no effect on human health.
However, in Poblado C-10 (Z-6) and Villa Aldama (Z-7) in the dry and rainy seasons there 11 were detected high oxygen values, which suggests that there exists primary productivity in

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In general pH was between 6.5 and 8, within limit allowed by Mexican Official Standard

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NOM-127-SSA1-1994, for Water for Human Consumption (  Table 3. pH, electric conductivity (CE), temperature (T°), total (C-T) and fecal (C-F) The values for total and fecal coliforms in the wells sampled were very high in regards to

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Salts concentrations (Na 8.7 meq L -1 ), (Mg 8.33 meq L -1 ) and (Ca 5 meq L -1 ) in all wells 17 studied were below established limits; no reference, in the existent legal framework, has 18 been found relating to the maximum K levels in water for human consumption; the other 19 parameters studied were inside the limits allowed (

10
In fact, water generally was less polluted by nitrates in dry season (average was in 5.3 and 11 median in 4.4) than in the rainy and norte seasons, when nitrates concentration increased 12 almost twice (Table 5). Evidently, the increase in nitrates concentration coincides with 13 precipitation increase. Also, the study basin is characterized to contain a vast surface of

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Aquatic animals are more sensitive to ammonium than mammals. If we apply the 28 previously referred limit of 0.50 mg/L, almost all obtained values would be below it, which 29 would disguise the results obtained in relation to effect on aquatic organisms. Therefore, it Excepting station 1 of The Naranjeño river, and stations 1, 2 and 3 of The San Felipe river 1 which quantities were non-detectable in dry season, the same as for station 3 of The 2 Naranjeño river and station 3 of The Santa Ana river in that of the norte season, in general, 3 in all seasons, very high levels of ammonium were observed. These levels are very superior 4 to the maximum tolerance for fish (Table 5).

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Only the station 1 of The Santa Ana river showed slightly lower levels (0.08) in dry season.

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As in the case of nitrates and ammonium, values were lower in dry season.

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A progressive increase was detected in residual chlorine levels from the dry season to that of 28 the rainy season. In the first case, only sample station 3 The Santa Ana river had levels above 29 standard in two depths.

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In the rainy season there were 5 stations that surpassed allowed limits (3 The Naranjeño    The turbidity can cause a decrease in water O2 concentration, with a rising negative effect on 1 fish, and reduction of light penetration in water column, which diminishes rate of 2 photosynthesis activity and, consequently, it reduces the primary productivity of the 3 phytoplankton that is the aquatic animals basic food.

4
A primary productivity reduction can collapse at superior trophic levels. On the other hand, 5 turbidity could also negatively affect populations of invertebrates and to interfere with 6 behavior, feeding and growth of many fish species and cause damages, due gills abrasion 7 and obstruction; it has also been found that increases the susceptibility of fish to illnesses, 14 In general, there were found levels much below this limit in almost all sampling stations and 15 seasons (        (Table 7).

3
The maximum value reached was 2400 NMP/100 ml. In rainy and norte seasons 4 concentration of total and fecal coliforms decreased dramatically, in fact, in The Naranjeño 5 river permissible levels were reached in these two seasons, while in The Santa Ana river this 6 was only obtained in norte season. The San Felipe river was still classed as polluted, during 7 the norte season. Coliforms reduction observed in rain and norte seasons was due to 8 increases of water volume, these organisms are then dispersed and head out to sea.

9
The coliforms presence in the basin is of supreme importance for environmental and human

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The behavior for Na levels was similar, the smallest corresponded to The Naranjeño river,

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but the season of lowest concentration was the dry season.

20
In the season of rains there were very high concentrations in the rivers Santa Ana and San

2
In most of the sampling sites nitrates were found in non-detectable quantities, however, 3 these increased until surpassing reference value in rain season (Table 9) Table 9. Values of nitrates, ammonium, phosphates and chlorine in the seven lagoons 16 studied.
In water, ammonium can be shown in two chemical species whose proportion depends on 1 hydrogen potential (pH) and temperature. One of them is ionized ammonium or NH 4+ and values exceeded maximum limits for protection of seawater life in The Ecological Criteria.

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Except for some few cases, mainly in dry season, turbidity generally stayed below the 40 30 NTU that is maximum acceptable for development of aquatic communities, according to 31 water contamination control (UNESCO, 1995) (Table 10). This was expected due continuous 32 exchange of fresh water and salt water with the sea 'allows diluting' organic matter coming 33 from rivers.

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In general, in the lagoons studied there were found to be appropriate levels of O2 in dry and     (Table 11).

13
The same as for rivers, concentrations of total and fecal coliforms were extraordinarily high   Table 11. pH, electric conductivity, temperature, and total and fecal coliforms values in the 5 seven lagoons studied.

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The most polluted lagoons, whose higher values surpassed the standard in dry and rainy 7 seasons were El Paso del Ostión, Las Palmas and Cocal, because they are water bodies 8 which are relatively closed and that only have communication with other lagoons in 9 growing season, between October and November, which means that in dry season they do not receive replacement of sea water, and this is the reason why nutrients and 11 microorganisms remain concentrated.

12
Presence of high concentrations of total and fecal coliforms in lagoons studied represents a 13 serious problem for regions economic activities, in principle because fishing is an important being of high commercial value, it is seen that in the region, it reaches only marginal prices 1 due to accumulation of coliforms consequence of their screening food habits.  problem of public and environmental health that seems not to be studied by the involved 10 sectors.

11
Sources of water chemical contamination in the basin are nitrates and the phosphates. The

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presence of nitrates in wells for human consumption can represent a continuous risk for 13 population, since impact can occur in long term and to go unseen by the population.
14 Nitrates, ammonium and phosphate concentrations in natural water bodies were very high.

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Although scope of this study did not contemplate to measure effects on the biological 16 community in the locations studied, there is solid evidence that levels similar to the ones 17 found in the area have an adverse effect on fauna and water productivity. The negative 18 outcome to environmental and to economic activities is unknown, but, according to similar 19 studies, it could be considerable.

20
Concentrations of organic and inorganic pollutants tend to increase in the rainy and norte 21 seasons due to run off of urban and agricultural organic residuals due the rain flows.

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Concentrations of these pollutants were smaller in lagoons that are connected to sea due to 23 water exchange between both systems.    © 2012 The Author(s). Licensee IntechOpen. This is an open access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.