Loss of macronutrients (N, P, K) in the hydrographic basin of the River Ivaí, an affluent of the River Paraná

Abstracts

Influence of some environmental variables in the loss of macronutrients N, P, K, from the hydrographic basin of the River Ivaí were analysed. Water samples of the river were monthly collected for five consecutive days during a year. In terms of total intervals of average monthly values and total average values experiment results, in mg L-1, were: N (0.32-3.22 and 1.65); K (0.73-2.69 and 1.38); P (not detected-0.39 and 0.076); COD (0.21-36.0 and 12.8); O2(dis) (1.89-8.40 and 5.43); and temperature (ºC) (16.0-30.8 and 24.6); pH (5.18-8.50 and 7.15). Statistical analysis of data showed that quantity of macronutrient (N, K, P) carried off from the hydrographic basin of the River Ivaí were directly correlated to fluviometric levels (caused by rainfall and floodings) at 5% level of significance. Carried off quantities, in t a-1, were N = 25,136.0; K = 21,010.0 and P = 1,161.2.

Erosion; macronutrients; hydrographic basin; environment

Neste estudo foram analisadas algumas variáveis ambientais que influenciam a perda de macronutrientes (N, P e K) na bacia hidrográfica do rio Ivaí, afluente do rio Paraná. As amostras compostas de água foram coletadas mensalmente, em 5 dias consecutivos, durante um ano. No ato da coleta foram medidos, o pH, a temperatura, o O2(dissolvido) e os níveis fluviométricos. O N total foi determinado pelo método de Kjeldahl. Após a digestão das amostras com redução de volume foram determinados, o P total, pelo método espectrofotométrico do UV-Vis com ácido ascórbico e o K total pela técnica da espectrometria da absorção atômica. O DQO foi determinado pelo método da oxidação da matéria orgânica pelo K2Cr2O7, em excesso, em ácido sulfúrico concentrado. Em termos de intervalos das médias mensais, média global, os resultados experimentais foram os seguintes, em mg L-1: N (0,32-3,22 e 1,65); K (0,73-2,69 e 1,38); P (não detectado-0,39 e 0,076); COD (0,21-36,0 e 12,8); O2(diss) (1,89-8,40 e 5,43); e, temperatura (ºC) (16,0-30,8 e 24,6); pH (5,18-8,50 e 7,15). A análise estatística dos dados mostrou que a quantidade de cada macronutriente levada pelas águas do rio Ivaí é diretamente correlacionada aos níveis fluviométricos do rio, em nível de 5% de confiança. As quantidades perdidas em t a-1 foram: N = 25.136,0; K = 21,010,0 e P = 1,161,2, respectivamente.

ENGINEERING AND TECHNOLOGY

Loss of macronutrients (N, P, K) in the hydrographic basin of the River Ivaí, an affluent of the River Paraná

Deborah Maria Corrêa Guiraud^I; Ervim LenziII, ^*; Eduardo Bernardi Luchese^II; Luzia Otília Bortotti Fávero^II

^IDepartamento de Química; Universidade Federal do Paraná - UFPR; Curitiba - PR - Brazil

IIDepartamento de Química; Universidade Estadual de Maringá - UEM; Av. Colombo, 5970; 87020-900; Maringá - PR - Brazil

ABSTRACT

Influence of some environmental variables in the loss of macronutrients N, P, K, from the hydrographic basin of the River Ivaí were analysed. Water samples of the river were monthly collected for five consecutive days during a year. In terms of total intervals of average monthly values and total average values experiment results, in mg L^-1, were: N (0.32-3.22 and 1.65); K (0.73-2.69 and 1.38); P (not detected-0.39 and 0.076); COD (0.21-36.0 and 12.8); O_2(dis) (1.89-8.40 and 5.43); and temperature (⁰C) (16.0-30.8 and 24.6); pH (5.18-8.50 and 7.15). Statistical analysis of data showed that quantity of macronutrient (N, K, P) carried off from the hydrographic basin of the River Ivaí were directly correlated to fluviometric levels (caused by rainfall and floodings) at 5% level of significance. Carried off quantities, in t a^-1, were N = 25,136.0; K = 21,010.0 and P = 1,161.2.

Key words: Erosion, macronutrients, hydrographic basin, environment

RESUMO

Neste estudo foram analisadas algumas variáveis ambientais que influenciam a perda de macronutrientes (N, P e K) na bacia hidrográfica do rio Ivaí, afluente do rio Paraná. As amostras compostas de água foram coletadas mensalmente, em 5 dias consecutivos, durante um ano. No ato da coleta foram medidos, o pH, a temperatura, o O_{2(dissolvido)} e os níveis fluviométricos. O N total foi determinado pelo método de Kjeldahl. Após a digestão das amostras com redução de volume foram determinados, o P total, pelo método espectrofotométrico do UV-Vis com ácido ascórbico e o K total pela técnica da espectrometria da absorção atômica. O DQO foi determinado pelo método da oxidação da matéria orgânica pelo K₂Cr₂O₇, em excesso, em ácido sulfúrico concentrado. Em termos de intervalos das médias mensais, média global, os resultados experimentais foram os seguintes, em mg L^-1: N (0,32-3,22 e 1,65); K (0,73-2,69 e 1,38); P (não detectado-0,39 e 0,076); COD (0,21-36,0 e 12,8); O_2(diss) (1,89-8,40 e 5,43); e, temperatura (⁰C) (16,0-30,8 e 24,6); pH (5,18-8,50 e 7,15). A análise estatística dos dados mostrou que a quantidade de cada macronutriente levada pelas águas do rio Ivaí é diretamente correlacionada aos níveis fluviométricos do rio, em nível de 5% de confiança. As quantidades perdidas em t a^-1 foram: N = 25.136,0; K = 21,010,0 e P = 1,161,2, respectivamente.

INTRODUCTION

The 16^th World Congress of Soil Science emphasized the relationships between human societies and the soil cover. Among these relationships, soil and water conservation are well identified challenges, which have given rise to more than 50 years of research on soil erosion around the world. One of the main concerns is to allow sustainable soil cultivation (Auzet et al., 2001).

Intense directionless occupation of soils in agriculture leads to imbalanced ecology. One of the greatest negative environmental impacts produced by such occupation is the process of soil erosion (Cerdan et al. 2002; Van Muysen and Govers, 2002; Usón and Ramos, 2001; Zhou and Zhu, 2001) and the consequent lixiviation of nutrients to the rivers (Drechsel et al, 2001; Sequi et al., 1991; Bittencourt, 1982), causing eutrophication of the water body (Withers and Lord, 2002; Jaworski et al., 1992; Rosensteel and Strom, 1991; Esteves, 1988). It may also cause contamination and pollution of the environment (Manahan, 1994; Rose et al., 1991; Rossi et al., 1991) and cause a potential health hazard (Withers and Lord, 2002).

The capacity of mankind to produce food and live in an unpolluted environment depends on their ability to control the speed at which soil erosion is taking place (Poesen, 1996). Key factors upon which models of soil erosion are based for global changes are climate and atmospheric CO₂ concentration that affects the hydrologic cycle and erosion caused by water and wind (Williams et al., 1996). Erosion is thus the main soil deterioration factor caused by humans. It is the principal threat to sustainable management of soil (Ingram et al., 1996). Sustainable agriculture and its controversies have been headlined in the last few years (Hoag and Skold, 1996; Lee, 1996; Thompson and Pretty, 1996). Blair and McSherry (1996) state that the philosophical nucleus of sustainable agriculture is an ethical injunction in which the management of landscape inter-transformation and earth resources, soil, energy, water, air, biota diversity, etc, are taken into account.

Within this range of philosophy, techniques have been developed in the last few years throughout the world for the correct use of soil. To minimization the effects of erosion and soil degradation were proposed several techniques for soil manipulation, such as, contour hedging, contours with permanent grass, direct plantation, crop rotation, use of geosynthetic mulching mat and others (Ahn et al. 2002; Chisci, et al. 2001; Malik et al. 2000; Dewald, 1996; Alegre and Rao, 1996; Dalton et al., 1996; Midimore et al., 1996; Perret et al., 1996; Wyland et al., 1996; Kloke, 1996).

General Aspects of the River Ivaí Basin

The River Ivaí is an affluent of the River Paraná, upstream Itaipu dam, and has a hydrographic basin of 36,000 km² within the state of Paraná (Brazil) containing excellent lands for agriculture and pasture. Some of its micro-basins have model soil management (Busscher et al., 1996). There are almost no forests in the basin and climate is temperate. Average yearly rainfall is 1,500 mm with January, February and March as the most rainy months.

The following data on the River Ivaí basin were supplied by DNAEE-ITAIPU:

• Due to abundant rainfall and good soil conditions the basin surface drainage is considerable when specific discharge ranging from 17 to 20 L s

  ^-1 km

  ^-2 along the basin is taken into consideration.

• Long range average discharge of the River Ivaí at the beginning of the lower stretch in Porto Paraíso do Norte is 483 m

  ³ s

  ^-1 for 1954-1981. Due to rainfall distribution throughout the year a clear seasonal regularity of average monthly discharges has not been observed.

• Floodings occur with great intensity and throughout the year. The highest value reaching 6,072 m

  ³ s

  ^-1 was observed in Porto Paraíso do Norte.

The aim of this work was to evaluate of loss of macronutrient N, P and K occurring naturally by erosion lixiviation and percolation of the River Ivaí basin and identification of the possible dependence with some environmental responsible variables.

MATERIALS AND METHODS

Site, periodicity and sample form

According to data of The National Department of Water and Electricity (DNAEE), 30 fluviosedimentometric stations are present along the River Ivaí. The station at Paraíso do Norte, Figure 1, was chosen owing to its 90-km distance from Maringá, Paraná, making daily collections feasible during five days and repeated monthly throughout the year (WMO, 1988). From the composed water samples, 1.5 L aliquots were separated for each element (N, P, K and COD - Chemical Oxygen Demand). Precautions were taken with regard to representative character of the composite samples (Keith, 1996), cleaning of material and contamination avoidance (WMO, 1988; Moody and Linstron, 1977); type of material used in collection, storage and sample conservation (Bartram and Balance, 1996; Souza and Derísio, 1977; Wagner, 1976; Mart, 1979).

Variables measured during collection

Temperature, pH, concentration of DO (Dissolved Oxygen) and river level on the limnimetric scale of the station were measured and or registered during collection.

Analysis of total Nitrogen (N)

Nitrogen was characterized as total N by Kjeldahl method (Horwitz, 1980; CETESB, 1978a).

Analysis of total Phosphorus (P)

Samples were initially digested with sulphuric acid - ammonium persulphate. Measurement of phosphorus (PO₄^3-) concentration was made by spectrophotometric method UV-VIS of ascorbic acid, ammonium molybdate and potassium antimoniltartarate at l = 880 nm using Spectrophotometer (GBC UV-VIS 918), (Horwitz 1980; CETESB, 1978b).

Analysis of total Potassium (K)

Samples were pre-concentrated and digested with concentrated HNO₃ (Horwitz, 1980). Potassium concentration was determined by atomic absorption spectrometry, by Spectrometer (AA CG 7000 ABC, Scientific Instruments Ltd). (Welz and Sperling, 1999; CETESB, 1978c).

COD

Samples were digested with the excess of potassium dichromate in a strong acid environment (H₂SO₄) in ebullition and with reflux system for two hours. After cooling, excess of dichromate was titrated with ferrous sulphate with ferroin as indicator (Braile and Cavalcanti, 1993).

Statistical analysis

Data were submitted to statistical analysis of variance and linear correlation (Costa, 1997; Gomes, 1987).

RESULTS AND DISCUSSION

Table 1 shows the average monthly values, in mg L^-1, of N; K, and P corresponding to values of daily collection samples (5 days per month) analysed in triplicates and the fluviometric levels (FL) corresponding to averages measurement of the limnimetric scale in the fluviosedimentometric station of Paraíso do Norte. Table 2 shows monthly average values of COD measurements and corresponding values of pH, temperature and dissolved oxygen in water samples.

River Ivaí basin

During the year, in which samples were taken, periods of drought and heavy rainfall besides normal periods of climate occurred in the basin. Agriculture had its normal stages of soil preparation, plantation and harvest. Soil with or without grass covering was under observation. In the region under analysis, there were cane sugar plantations and burnings as a consequence.

Severe frosts occurred with loss of pastures and cereal plants. In the spring, a prolonged drought delayed the plantation till the end of November, leaving the plowed lime-rich soil without any vegetation waiting for rain for approximately 90 days. Characteristics of such climate were average annual temperatures between 24⁰C and 26⁰C, confirmed by overall average annual value of 24.6⁰C (Table 2).

Macronutrients N, P and K

The variance analysis for each macronutrient concentration at 5% level of significance for time variation factor (month of collection), showed significant difference for the three macronutrients. The high values of standard deviation (s) presented in Table 1 and Table 2 mainly for some measured variables, for example, the COD, showed this temporality. An analysis of linear correlation of concentrations of each macronutrient together with fluviometric levels showed the following indexes of linear correlation [r = (R²)^1/2]: N (r = 0.509), Figure 2; P (r = 0.770) Figure 3; and K (r = 0.859) Figure 4. At 5% level of significance there was a positive correlation between the variables. This showed losses of macronutrients with floodings, indirectly reflecting the influence of erosion and finally the river basin degradation. At 5% levels of significance, the variables (COD, pH, temperature and O_2(dis)) of water samples did not affect the concentration of the macronutrients. It was interesting to observe that at 10% level of significance temperature of samples was correlated negatively with concentrations of macronutrients.

Analysing average values of FL (Table 1) and average values of respective temperatures (Table 2), it was found that during periods of lower temperature there occurred the highest fluviometric levels, thus explaining the negative relation.

COD values were directly proportionate to the level of organic matter and presented positive correlation with the concentration of macronutrients analysed only at 20% level of significance.

Average annual total concentrations of the three macronutrients in water in the sequence N, K and P were in the proportion 21.6:18.9:1.00. P concentration was 20 times less than that of N and K. This was due to fixation of phosphorus by iron, aluminum and manganese compounds (Brady, 1989). The chemical equations [01], [02] and [03] show the reactions of P retention in soil or in particulates dispersed in water and or precipitated.

It becomes less available in soil solution and consequently less eroded, lixiviated and percolated than N and K (Malavolta, 1981). Loss by erosion, lixiviation and percolation chiefly depends on quantity of rainfall (Withers and Lord, 2002; Chisci et al. 2001; Zhou and Zhu, 2001).

Amounts of N, P and K carried off the River Ivaí basin could be estimated when total annual average (N = 1.65; P = 0.076; K = 1.38, mg L^-1 respectively) and the average discharge of the River Ivaí for the period 1954-1981 (483 m³.s^-1) were taken into consideration.

The results were N = 25,136.0 t a^-1; K = 21,020.0 t a^-1; P = 1,162.2 t a^-1 and were compatible to those for the Rivers Baía and Paraná in the region of Porto Rico, Paraná (Lenzi et al., 1992).

The macronutrients losses decrease the soil fertility and consequent productivity. These quantities may be lessened by means of correct soil management achieved by instructions to farm workers, such as contour hedging, contours with permanent grass, direct plantation, crop rotation, etc. The nutrients increase in the water river cause the eutrophication.

CONCLUSIONS

From the analysis and discussion of data, the following conclusions may be taken:

• Average monthly quantities of N, P, K in the River Ivaí differed from one another significantly at 5% significance.

• The same averages showed positive linear correlation (r) with their respective fluviometric levels at 5% level, showing higher losses in flooding period.

• At 5% level of significance, influence of COD, pH, temperature and dissolved oxygen was not observed in the water samples on the respective quantities of N, P, and K carried away by the Ivaí waters.

• Proportion of N, P, and K quantities carried away by the waters was 21.6

  :18.9

  :1.00, respectively.

• In terms of average annual values, quantities of N, P, K carried away from the basin were N = 25,136.0 t a

  ^-1; K = 21,010.0 t a

  ^-1 ; P = 1,162.2 t a

  ^-1.

ACKNOWLEDGEMENTS

The research team would like to thank the Chemistry Department, the Environmental Multidisciplinary Studies Group (GEMA), the Research Nucleus in Limnology, Ichthyology and Aquiculture (NUPELIA) of the State University of Maringá, the Chemistry Department of the Federal University of Paraná and to CAPES.

Received: June 21, 2002

Revised: October 16, 2003

Accepted: May 10, 2004

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*

Author for correspondence

Publication Dates

• Publication in this collection
  31 Aug 2004
• Date of issue
  Aug 2004

History

• Accepted
  10 May 2004
• Reviewed
  16 Oct 2003
• Received
  21 June 2002