Agriculture Reference
In-Depth Information
total HM in soils and available HM for plants (extracted by 0.1M HCl)
(Wang et al, 1994). The C values were used as guidelines for assessment of
HM in soils.
Statistical analysis of the data
Data were subjected to an analysis of variance and means were compared by
Fisher's protected least significance difference (LSD) test. Statistical analysis
was carried out with assistance of CIPSTAT7 (CIP Statistical Analyser)
developed at the International Potato Center. Descriptive statistics were used
to explain the basic features of the data in a study to provide simple
summaries about the samples.
R ESEARCH F INDINGS AND D ISCUSSIONS
Historical contamination of R´mac River
The incorporation of spatial-temporal data on water quality in a geographical
information system (GIS) proved to be a useful tool in assessing pollution
trends for different metals in different parts of the watershed and the
associated potential risks. As the maps track changes over time, they are
useful in identifying trends and offer a general idea of what is influencing their
concentrations throughout the Rı´ mac River. Looking at these summary maps
is faster and easier than doing extensive detailed analysis of the raw water-
quality data. Also, they help to focus the analysis directly on areas of concern,
locate areas of high risk due to the presence of HM and FC and assesses the
discrepancies between different data sets.
Figure 7.3 shows the annual averages over time of As, Cd, Cr, Pb and FC
reported by SEDAPAL (1997-2004) and DIGESA (2000-2004), while Figure
7.4 shows the spatial distribution of As, Pb and FC along the Rı ´ mac river
corresponding to the year of greatest contamination (2000 or 2001) and the
last reported (2004).
Cd and Cr did not affect any part of the basin and were always below the
maximum permissible level for vegetable irrigation. However, vegetable
growing areas in the lower part of the basin were affected with contaminated
water for at least two years with As (2000 and 2002) and for the entire
evaluated period with Pb (1997-2004).
As expected, the presence of Pb and As in the Rı´ mac River is related to
discharges of mining wastes in the upper and middle part of the basin (Infante
and Sosa, 1994; MEM-DGAA, 1997). The data also indicates that As levels
have reduced in the last two years (2003-2004) (Figure 7.5A). This is probably
due to an obligatory implementation of the Environment Adequacy Program
(Programa de Adecuacio´ n Ambiental, PAMA), as applied to ongoing mining
operations and the Environment Impact Assessments which are applied to
new mine operations (MINEM, 1993). However, there is no evidence that
water quality has been improved in terms of Pb (Figure 7.5B). High levels of
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