Nutrient stream attenuation is altered by the duration and frequency of flow intermittency

River flow intermittency affects physical and biological processes in lotic ecosystems, including nutrient attenuation and therefore water purification. We investigated the effect of river flow intermittency, including its duration and occurrence frequency, on the attenuation of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (P-PO43-). The net balances of each nutrient form were assessed in artificial streams colonized by biofilms and exposed to six treatments resulting from the combination of two flow intermittency durations (28 or 56 days) and three intermittency frequencies (one, two or four interruption episodes). The respective influences on the nutrient balances were assessed one and eight days after flow resumption, with negative or positive balances indicating net consumption or production, respectively. The P-PO43- balances ranged from -50.3 to -15.7 mu g P-PO43- h(-1) m(-2), while for the components of DIN, they varied between -135.6 and -7.3 mu g N-NH4+ h(-1) m(-2) (ammonium), -1.4 and 4.2 mu g N-NO2- h(-1) m(-2) (nitrite) and -39.1 and 18.6 mu g N-NO3- h(-1) m(-2) (nitrate). In general, longer non-flow durations impaired nutrient attenuation. Overall, while each nutrient form showed specific patterns, our experiment indicated that (1) nutrient attenuation usually decreased with longer non-flow durations, (2) attenuation generally recovered after frequent events of water flow resumption and when rewetting was longer and (3) longer desiccation periods seemed to persistently affect the biogeochemical responses regardless the number of times flow returned to the system. Our results highlight that more severe conditions (causing dehydration of the substrates and inhibition of biofilm activity) might strongly affect the biogeochemical functioning of temporary streams, with important management implications under accelerating global changes.

Automated summary

The intermittent flow of the river affects the attenuation of nutrients in lotic ecosystems. Longer periods of non-flow negatively impact nutrient attenuation, but recovery can occur with frequent water flow resumption and longer rewetting periods. Extended desiccation periods have a persistent effect on biogeochemical responses in temporary streams, regardless of the frequency of flow resumption.