Michael B. Flinn

Microbial Biogeography of Arctic Streams: Exploring Influences of Lithology and Habitat

Terminal restriction fragment length polymorphism and 16S rRNA gene sequencing were used to explore the community composition of bacterial communities in biofilms on sediments (epipssamon) and rocks (epilithon) in stream reaches that drain watersheds with contrasting lithologies in the Noatak National Preserve, Alaska. Bacterial community composition varied primarily by stream habitat and secondarily by lithology. Positive correlations were detected between bacterial community structure and nutrients, base cations, and dissolved organic carbon. Our results showed significant differences at the stream habitat, between epipssamon and epilithon bacterial communities, which we expected. Our results also showed significant differences at the landscape scale that could be related to different lithologies and associated stream biogeochemistry. These results provide insight into the bacterial community composition of little known and pristine arctic stream ecosystems and illustrate how differences in the lithology, soils, and vegetation community of the terrestrial environment interact to influence stream bacterial taxonomic richness and composition.

Macroinvertebrate and zooplankton responses to emergent plant production in upper Mississippi River floodplain wetlands.

The upper Mississippi River is managed as a multiple use system, balancing the needs of industry, recreation, and navigation. Through water-level management (WLM), the U. S. Army Corps of Engineers manipulates water levels in some navigation pools to promote emergent vegetation for fish and wildlife in off-channel habitats. A manipulative experiment was conducted to assess responses of invertebrates to vegetation and associated organic matter associated with WLM in floodplain wetlands of Mississippi River navigation pool 25. Macroinvertebrate and zooplankton communities and benthic organic matter were compared in replicated paired plots consisting of experimentally de-vegetated and adjacent control plots. Hydrology was variable during the study, resulting in a strong vegetation response year (1999), a no response year (2000), and a moderate response year (2001). Differences in benthic organic matter between plot types were most pronounced in fall 2000, following the strong vegetation response year, where residual vegetation resulted in significantly higher total and coarse benthic organic matter in vegetated plots. Of the 2 years (2000, 2001) they were sampled, differences in macroinvertebrate communities were only evident in 2001 when there was a moderate vegetation response. Total macroinvertebrate densities during 2001 were similar between devegetated and vegetated plots, but responses of individual taxa varied. Total macroinvertebrate biomass was significantly higher in the vegetated plots during 2001. Of dominant groups, Oligochaeta biomass was significantly higher in vegetated plots, whereas total Chironomidae abundance and biomass were both significantly higher in devegetated plots. Community metrics reflected higher macroinvertebrate diversity in vegetated plots. Zooplankton were not abundant or diverse in plots, but total densities were significantly higher in vegetated plots during the 1999 strongest vegetation response year. Results demonstrate that WLM to enhance emergent vegetation in off-channel habitats of this large river influences organic matter dynamics and invertebrates. Although many groups responded positively to vegetation, responses varied with the degree of vegetation response and the taxonomic resolution of analyses, suggesting that hydrologic variability, and associated spatial and temporal variability in emergent vegetation, can enhance invertebrate diversity in floodplain wetland habitats.

Assemblage-level estimation of nontanypodine chironomid growth and production in a southern Illinois stream

Abstract Chironomid midges are abundant and important components of freshwater communities, but estimating their production is problematic because of taxonomic difficulties, short generation times, and overlapping cohorts. We measured growth rates of nontanypodine chironomid larvae from a 3rd-order stream in southern Illinois, USA, at different temperatures to estimate assemblage-level production using the instantaneous growth method. We collected Chironomini, Tanytarsini, and Orthocladiinae larvae, separated them into small (0–3.9 mm), medium (4–7.9 mm), and large (8–12 mm) size classes, and then reared larvae in a controlled environment for 3 to 7 d at temperatures ranging from 5 to 28°C. We measured lengths of individual larvae before and after each trial and estimated biomass using a length–mass regression. Instantaneous growth rates (g) across all size classes ranged from 0.008 mg mg−1 d−1 at 5°C to 0.24 mg mg−1 d−1 at 22°C. Instantaneous growth rates of small larvae increased linearly with temperature between 5 and 22°C (r2 = 0.99, p = 0.0003). Instantaneous growth rates of medium and large larvae also appeared to increase linearly with temperature (medium: 5–22°C, large: 5–25°C), although power functions explained a greater proportion of the variance than linear functions (medium: r2 = 0.96, p = 0.004, large: r2 = 0.77, p = 0.05). We applied these models to data from monthly samples from the same stream and obtained an annual habitat-weighted production estimate of 4.2 g ash-free dry mass m−2 y−1 and an annual production to biomass ratio of 26. Application of 2 other assemblage-level chironomid growth models developed for headwater streams in the southern Appalachians yielded much different production estimates, illustrating the risks of applying these types of models to systems with different temperature regimes, taxonomic composition, or size spectra. Our temperature-specific models will enable more accurate estimates of chironomid production in central USA streams with thermal regimes and larval midge assemblages similar to those in Big Creek.

Continental-scale decrease in net primary productivity in streams due to climate warming

An increase in stream temperature leads to a convergence of metabolic balance, overall decline in net ecosystem productivity, and higher CO2 emissions from streams, according to analyses of temperature sensitivity of stream metabolism across six biomes.AbstractStreams play a key role in the global carbon cycle. The balance between carbon intake through photosynthesis and carbon release via respiration influences carbon emissions from streams and depends on temperature. However, the lack of a comprehensive analysis of the temperature sensitivity of the metabolic balance in inland waters across latitudes and local climate conditions hinders an accurate projection of carbon emissions in a warmer future. Here, we use a model of diel dissolved oxygen dynamics, combined with high-frequency measurements of dissolved oxygen, light and temperature, to estimate the temperature sensitivities of gross primary production and ecosystem respiration in streams across six biomes, from the tropics to the arctic tundra. We find that the change in metabolic balance, that is, the ratio of gross primary production to ecosystem respiration, is a function of stream temperature and current metabolic balance. Applying this relationship to the global compilation of stream metabolism data, we find that a 1 °C increase in stream temperature leads to a convergence of metabolic balance and to a 23.6% overall decline in net ecosystem productivity across the streams studied. We suggest that if the relationship holds for similarly sized streams around the globe, the warming-induced shifts in metabolic balance will result in an increase of 0.0194 Pg carbon emitted from such streams every year.