Ecosystem structure and function in two branches of an eastern Minnesota, USA, trout stream

Abstract

Among freshwater systems, coldwater habitats are among the most threatened by climate change. Examining the impacts of increasing water temperature requires the use of both traditional biomonitoring efforts and measures of ecosystem function and structure. We examined fish and macroinvertebrate communities, leaf decomposition rates, periphyton production, and ecosystem metabolism to compare two branches of a trout stream in Minnesota with differing thermal regimes. The cooler South Branch had more coldwater fish, a higher index of biological integrity for fish but a lower index for macroinvertebrates. There were no differences in leaf decomposition rates between branches, although nonnative buckthorn leaves decomposed faster than native black cherry leaves. Periphyton production was higher in the North Branch than the South Branch. Both branches had high nitrogen but low phosphorus levels. Nutrient enrichment with phosphorus enhanced periphyton production in both branches. Measures of stream metabolism, based on diurnal variation in oxygen levels, showed that both branches were heterotrophic. Despite higher periphyton production in the North Branch, gross primary production was higher in the South Branch. The bioassessment measures used in our study yielded inconsistent results, pointing to the need for multiple methods to examine and better describe potential responses to warming from climate change.

Influences of Terrestrial Inputs of Organic Matter on Coastal Water and Bottom Sediments in the Seto Inland Sea, Japan

“…The other is for measuring the concentrations of particulate organic carbon (POC) and particulate organic nitrogen (PON) and δ 13 C in POC, in which 200 mL ~ 1,200 mL of water passed through each filter, in order to acquire adequate POC for δ 13 C analysis. The glass filters for measuring the concentration of chlorophyll-a were kept submerged in 90% acetone each in 6 ml plastic tube to be quantified using a calibrated fluorometer (Trilogy; Turner Design, San Jose, USA), according to EPA Method 445.0 [21]. The glass filters for measuring the concentrations of POC and PON and δ 13 C in POC were dried in oven at 50°C and kept in a desiccator with 12 N hydrochloric acid for 24 hour in order to eliminate particulate inorganic carbon using hydrochloric acid vapor.…”