Biogeochemical processes controlling aquatic quality during drying and rewetting events in a Mediterranean non-perennial river reach

Nikolaos Th Skoulikidis; Leonidas Vardakas; Yorgos Amaxidis; Panagiotis Michalopoulos

doi:10.1016/j.scitotenv.2016.10.015

Biogeochemical processes controlling aquatic quality during drying and rewetting events in a Mediterranean non-perennial river reach

Sci Total Environ. 2017 Jan 1:575:378-389. doi: 10.1016/j.scitotenv.2016.10.015. Epub 2016 Oct 14.

Authors

Nikolaos Th Skoulikidis¹, Leonidas Vardakas², Yorgos Amaxidis¹, Panagiotis Michalopoulos³

Affiliations

¹ Institute of Marine Biological Resources & Inland Waters, Hellenic Centre for Marine Research, 46.7km Athens-Souniou Av., P.O. 19013, Anavissos, Attica, Greece.
² Institute of Marine Biological Resources & Inland Waters, Hellenic Centre for Marine Research, 46.7km Athens-Souniou Av., P.O. 19013, Anavissos, Attica, Greece. Electronic address: louisvard@gmail.com.
³ Institute of Oceanography, Hellenic Centre for Marine Research, 46.7km Athens-Souniou Av., P.O. 19013, Anavissos, Attica, Greece.

PMID: 27750134
DOI: 10.1016/j.scitotenv.2016.10.015

Abstract

Desiccation and re-flooding processes play a key role on hydrological features of non-perennial rivers. This study addresses the effects of these processes on the aquatic quality and unravels underlying biogeochemical processes of an intermittent river reach in southern Greece containing a spring-fed pool. Combined spatio-temporal sampling for physicochemical parameters, major ions and nutrients and high frequency automatic monitoring during a hydrological year (2010-2011) indicate that during the dry period, solute variation was controlled by "concentration" processes (i.e. evaporative concentration and high dissolved ion input from base flow sources). Metabolic and "concentration" processes appear intensified during desiccation and water temperature rise. Photosynthesis induced carbonate precipitation, while respiration increased with gradual desiccation, but did not cause carbonate dissolution. In certain cases, photosynthesis and respiration may have occurred simultaneously as a result of differing microhabitat metabolism within the same water body. However, during the entire desiccation cycle, autotrophic production exceeded respiration resulting in relatively high oxygen concentrations, even during the night. With increasing desiccation, a rise in nutrient assimilation occurred as well as ammonification and/or desorption of ammonium from sediments, with simultaneous loss of nitrate. During initial floods, flushing of carbonate phases was not significant. In contrast, initial flood events were characterized by the dissolution of very soluble salts, i.e. epsomite-type (MgSO₄∗7H₂O) and gypsum (CaSO₄∗2H₂O). Regarding sediment transport and nutrients, a 1000-times increase of suspended sediments was observed during re-flooding, while the nutrient quality degraded, particularly for N-species. Results of the current research may serve to better understand the links of hydrological and biogeochemical processes in non-perennial rivers and streams towards their efficient management and conservation.

Keywords: Biogeochemical processes; Carbonate precipitation; Desiccation; Epsomite dissolution; Non-perennial rivers; Nutrients; Photosynthesis; Re-flooding; Respiration.