Seasonal variability of nitrate flux in the Northern part of Karangbolong Karst Aquifer, Central Java

Kalisirah Springs and Jumbleng Spring are located in the northern part of Karangbolong Karst Area, Kebumen Regency. Tracer tests for underground rivers and field surveys indicate that the catchment areas of these two karst springs have the dominant land use of dry land farm and plantation. The condition of the catchment area will affect the chemical content of water resources in karst aquifers. Dry land farm and plantation use fertilizer in the process of planting, but in practice, there is nitrogen lost due to the washing process by rainwater. Karst landforms also have cavities and fissures that allow applied fertilizer to enter the karstic aquifer directly. This study aims to determine the nitrogen flux fluctuations in the form of nitrate (N) in Kalisirah Springs and Jumbleng Springs along with their relationship with discharge and rainfall. The data used in this study were primary data, which included data of the water level, rainfall, water chemistry samples, and the agricultural planting calendar. The N content was analyzed using hydrograph to determine the response of N flux to the discharge. Recording the amount of N used in agricultural activities in the catchment area was conducted by calculating the area of agricultural land use using Topographic Map of Indonesia, and the triangulation method was used to determine fertilizer characteristics in the catchment area. Kalisirah catchment area lost 56.09 N, while the Jumbleng catchment area lost 57.53 N. The extent of this loss is influenced by land use conditions which will have implications for the number and frequency of fertilization.