Whole-stream metabolism in nutrient-poor calcareous streams on Öland, Sweden

Abstract

We studied whole-stream metabolism in three headwater non-forested stream reaches on the island of Oland, Sweden in order to characterize the metabolism of this unusual ecosystem and to compare it with other stream ecosystems in NW Europe. Gross primary production (GPP) was generally low (<4 g O2 m−2 d−1) with the lowest GPP recorded in the most upstream, shallow reach draining the thin soils of the limestone Alvar plains. Here, completely flooded terrestrial plants could account for the whole primary production at baseflow. Ecosystem respiration (ER) increased several fold with agricultural impact, resulting in heterotrophic stream conditions downstream and higher light requirements for photosynthesis to outweigh respiration. A strong relationship between daily GPP and ER was found at the two most nutrient-poor sites. Temperature corrected instantaneous ER rate was highest in the beginning of the night, but decreased at the end of the night at the same reaches, indicating that dark respiration depleted photosynthetic products and became limited by organic substrates. The broad-scale comparison of open NW European streams showed a 1:1 relationship, indicating a tight link between daily GPP and ER during summer (April–August) but not during winter. This study has extended the range of GPP and ER measurements to include nutrient-poor NW European streams, thereby increasing the knowledge on stream metabolism in this, otherwise, highly agricultural impacted region. It also documented a strong relationship between GPP and ER in streams, ranging from extremely nutrient poor to moderately nutrient rich conditions during spring and summer.