High-frequency monitoring for the identification of hydrological and bio-geochemical processes in a Mediterranean river basin

A telemetric high-frequency hydrologic and water quality monitoring network was deployed to obtain data for the characterization of the hydrologic and bio-geochemical processes of a complex Mediterranean watershed of Koiliaris River, Crete, Greece. The network measures water level, water temperature, pH, dissolved oxygen (DO) and nitrate. Analysis of the hydrologic data suggests the existence of four hydrologic processes that operate in the watershed with distinctive characteristic response times. The response of the flow hydrograph of the upper reservoir of the Karstic system to a precipitation event had a characteristic time of 10 d while the characteristic time of the lower reservoir was 38 d. The flash flood events of Keramianos temporary river (tributary to Koiliaris) had a characteristic response time of 29 h while the diurnal variation of flow had a characteristic response time of 18 h. The diurnal fluctuation of the chemical parameters had a characteristic response time of 8 h for pH, 83 h for DO and 13 h for nitrates while the nitrate flush from the Neogene deposits to the river had a characteristic response time of 2.7 h. The diurnal fluctuation is related to in-stream biological activity. The results illustrate the importance of high-frequency sampling for accurate parameterization of processes operating in complex environmental systems with varying process response times.