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Response of Gammarus pulex and Baetis rhodani to springtime acid episodes in humic brooks
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Although the acid load has decreased throughout Scandinavia, episodic acidification continues to affect stream biology by temporarily decreasing pH levels and mobilising aluminium. These events are becoming more common as climate change renders more frequent and intense storm floods. The transient acidity can reduce fish populations, but fish food resources can also be impaired because macro-invertebrates are affected. In this in-stream study, two salmonid prey organisms (Gammarus pulex and Baetis rhodani) were exposed to snowmelt in six humic brooks with a natural gradient of pH and inorganic monomeric Al (Ali). We hypothesise that there are thresholds for acid toxicity that can be defined by mortality and changes in body elemental content. Mortality was observed and the whole body content of base cations (BC, i.e., Ca, Mg, Na and K) and metals (Al, Fe, Zn and Mn) were determined. Both species began to die and the total bodily BC content decreased as the pH levels decreased and the Ali concentrations increased. In contrast to what has been observed for fish gills, no accumulation of Al was observed. The invertebrate body Na content decreased when the pH level decreased, which indicated that the osmoregulation in both species was affected. The Ca content in G. pulex and the Mg content in B. rhodani diverged from the general BC-pattern by increasing when the pH level decreased. The mortality increased drastically at pH <6.0 and Ali >15 μg/L for G. pulex and at pH <5.7 and Ali >20 μg/L for the somewhat less sensitive B. rhodani. Although Ali is tightly correlated to pH, the local Al availability in soil and bedrock also affect the Al release and toxic Ali episodes can consequently arise in some catchment areas. The estimated values can be used as water quality thresholds to adjust lime dose because both Ali and pH levels have to be balanced to prevent harm in recovering stream ecosystems.

Keyword [en]
Thresholds Ali & pH; Gammarus pulex; Baetis rhodani; ionoregulation; liming strategy
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-80531OAI: oai:DiVA.org:su-80531DiVA: diva2:556272
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2012-09-25
In thesis
1. Toxicity of Inorganic Aluminium in Humic Streams
Open this publication in new window or tab >>Toxicity of Inorganic Aluminium in Humic Streams
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aluminium (Al) has been recognised as a main toxic factor alongside pH in acidified water ecosystems. The toxic effect of Al has been attributed to inorganic Al (Ali), though there are few in situ studies in ambient humic waters which are the focus of this thesis.

The aim was to estimate Ali toxicity and thus also Ali concentrations in Swedish humic streams. Subsequently it is necessary to analyse Ali correctly, which was studied by modelling and method intercalibrations. The hypothesis was that the effect of Ali could be followed via physiological effects and Al accumulation, as well as by mortality. Toxicity was studied by in stream exposures of brown trout (Salmo trutta L.) and two salmonid prey organisms (Gammarus pulex and Baetis rhodani) during spring flood.

The modelling of the Ali fraction was performed using monitoring data covering all of Sweden with satisfactory results. The essential variables for Ali modelling were determined; Al, DOC, pH and F, while Fe, Ca and Mg had less effect. The automated analytical procedure for Ali (with cation exchange followed by complexation with pyrocatechol violet) was modified and validated and showed to be the preferred method for laboratory analyses.

To avoid detrimental effects for brown trout Ali should be <20 µg/L and pH >5.0; mortality was high when the Ali was above 50 µg/L. The invertebrates were more sensitive, as mortalities occurred at pH <6.0 and Ali >15 µg/L for G. pulex, and at pH <5.7 and Ali >20 µg/L for B. rhodani. It is prudent to use a wide view and let the most sensitive species set the tolerance limits; a pH above 5.7-6.0 and Ali below 15-20 µg/L allows the stream ecosystems to thrive.

Today, as waters are recovering from acidification, the aim of mitigating liming is to carefully adjust dosage to avoid suboptimal water quality. The thresholds found in this thesis can be used to efficiently but carefully decrease liming, as both Ali and pH levels have to be balanced to sustain the recovering aquatic biota.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University, 2012. 42 p.
Keyword
Inorganic Al, toxicity, acidification, humic streams
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-80651 (URN)978-91-7447-577-7 (ISBN)
Public defence
2012-10-26, De Geer Salen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2012-10-04 Created: 2012-09-25 Last updated: 2012-09-25Bibliographically approved

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