Fate of phosphate and nitrate in waters of an intensive agricultural area in the dry zone of Sri Lanka

Abstract

The chemistry of surface waters and groundwater draining agricultural catchments in the north-central and northwestern areas of Sri Lanka is described. Hydrochemical data from 296 water samples are used to evaluate water quality and to identify the processes that control nitrate and phosphate concentrations in the water. The results indicate that nutrient concentrations in the groundwaters are greater than those in the surface waters. Increased nutrient levels were observed in groundwater in a selected area in the fortnight following fertilizer application. Detailed geochemical investigations of selected groundwater samples reveal a gradual rise of nitrate-N and other solutes along the horizontal flow direction. Compared to the application rates of fertilizer in the area, the average nutrient concentrations in all waters are relatively low (1.5 mg/l nitrate and 0.5 mg/l phosphate) and stable. The results suggest that prevailing reducing conditions, iron-rich overburden soil cover and manmade canal networks control nutrient accumulation in the groundwater.

Vulnerability of Coastal Aquifers Due to Nutrient Pollution from Agriculture: Kalpitiya, Sri Lanka

“…However, compared with the higher input of nitrate in to the groundwater low iron content indicates the lower reduction rates of iron in the aquifer due to the higher oxygen content supplied into the highly permeable sand by intense watering. In contrast, reducing condition which is observed in clayey soil areas control the input of nitrate into the groundwater by conversion them into nitrogen and therefore recorded nitrate values show lower figures, although the nitrate fertilizers are applied intensively (Young et al 2010;Gunatilake andGunatilake 2004, Pitawala et al 2007). The measured nitrate concentrations were converted into Nitrate-N values…”

“…This situation is facilitated by the consecutive cultivations throughout the year. In contrast, seasonal cultivations are carried out in the other areas of the country where the lower nutrient values are recorded (Young et al 2010;Gunatilake and Gunatilake 2004). Steady or even higher fluxes of nitrate can be expected into ground water during rainy season because farmers tend to almost double the fertilizer application during this period to supplement the infiltration losses.…”

Groundwater Quality

“…The N and P concentrations in the King Abdullah Canal were higher than the eutrophication level (Alkhoury et al, 2010). An increase in plankton counts was also (Young et al, 2010). The elevated nutrient levels in groundwater could be attributed to fertilizer application.…”

“…Surface waters and groundwater draining agricultural catchments in the north-central and northwestern areas of Sri Lanka were collected for nutrient analyses(Young et al, 2010). The elevated nutrient levels in groundwater could be attributed to fertilizer application.The use of swine manure and commercial fertilizer (ammonium nitrate) could also affect leaching of phosphorus to subsurface drain water under a corn-soybean rotation(Hoang et al, 2010) Rozemeijer et al(2010).…”

Seasonal variation of water quality parameters in different geomorphic Channels of the upper Malwathu Oya in Anuradhapura, Sri Lanka

“…Irresponsible and excessive application of fertilizer introduce large amounts of nutrients to water bodies; this is especially the case in paddy cultivation (Dissanayake & Weerasooriya, 1987). Young et al (2010) stated that the fertilizer application is high in North Central part of Sri Lanka amounting to six to ten times in excess of the levels recommended by the government. It was clearly observed that intense agricultural practices increase NO 3 ⁻ and PO 4 3 ‾ concentrations as well as other dissolved ions in groundwater (Young et al, 2009;Sutharsiny et al, 2012).…”