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

Abstract

This study focuses on spatial and temporal nutrient pollution of groundwater in the unconfined sandy aquifers of Kalpitiya peninsula, Sri Lanka, where agricultural activities are intense. The study covers two consecutive dry and rainy seasons during the period from 2008 to 2010. Nitrate is the dominant nutrient pollutant in groundwater. The values of Nitrate-N contents ranged from 0.60 to 212.40 mg/L in the dry seasons and 0.20-148.50 mg/L in rainy seasons. Phosphate in groundwater ranged from 0.20 to 5.70 mg/L in dry seasons and 0.04-10.35 mg/L with few exceptions in rainy seasons. About 50% of the studied water samples had Nitrate-N concentrations above WHO drinking water guideline values both in dry and rainy periods. These high concentrations were recorded from wells in agricultural lands. Although there is a slight decrease in the Nitrate-N concentrations at random in rainy seasons, an increasing trend of average concentrations became evident over the study period as a whole, probably indicating building up of Nitrate-N in groundwater in the vegetable growing areas. The spatial distribution of Nitrate-N too shows a good match of high Nitrate-N bearing zones with vegetable cultivated areas indicating intensive leaching from application of excessive chemical fertilizers. High Nitrate-N zones also showed fairly steady lateral distribution indicating slow lateral mobility of Nitrate-rich groundwater probably due to low hydraulic gradients. Low phosphate concentrations in both groundwater and surface soils either indicates their less use in the area or that the available phosphate is leached and removed from the aquifer water and (sandy) soil solutions and probably adsorbed in clayey deeper horizons. Low concentrations of major cations (especially K, Ca, and Na) indicate less impact on cation concentrations in groundwater by the fertilizer application or sea water intrusions/up-coning.

Managing shallow aquifers in the dry zone of Sri Lanka

“…In the islands off the peninsulas, 50 % of the wells contained nitrate levels above 10 mg/l. Other studies have found high levels of nitrate-N in groundwater (Mikunthan and de Silva 2009;Jeyaruba and Thushyanthy 2009), which have been directly related to agricultural activities ( (Jayasingha et al 2011;Liyanage et al 2000); Kuruppuarachchi and Fernando 1999;(Nagarajah et al 1988)). Overextraction of groundwater resources has also contributed to saltwater intrusion and higher nitrate loads in the groundwater (Jayasekera et al 2011;Jayasekera 2007).…”

Ammonium occurrence in a salinized lowland coastal aquifer (Ferrara, Italy)

“…Nitrogen (N) enrichment is responsible for the deterioration of water quality and health hazards (World Health Organization, ; Gelberg et al ., ; Gulis et al ., ), such as eutrophication (Howarth and Marino, ; Jayasingha et al ., ) and algal growth (Linderfelt and Turner, ).…”

Fate of urea fertilizers in sandy aquifers: laboratory and field case study from Kalpitiya, Sri Lanka

“…Groundwater contamination in terms of nitrate pollution in the area has been studied for several decades (Lawrence & Kuruppuarachchi, 1986;Mubarak et al, 1992;Kuruppuarachchi & Fernando, 1999;Liyanage et al, 2000). Recent investigations revealed that nitrate levels in groundwater at some places in Kalpitiya agricultural fields is as high as 212 mg/L during dry periods and more than 50 % of the studied wells have nitrate levels exceeding the WHO allowable limits (Jayasingha et al, 2011). It was also found that the nitrate accumulation rate is 2.3 mg/L per year for the last 10 year period.…”

“…The Kalpitiya agricultural field is an active and dynamic environment because the area is extensively fertilized and intensively watered (Jayasingha et al, 2011). Despite the semi arid conditions of the area, the sandy soil of the agricultural areas retains soil moisture for a considerable period during daytime due to watering.…”