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Hotchkiss, Erin R.
Alternative names
Publications (8 of 8) Show all publications
Jonsson, M., Hedström, P., Stenroth, K., Hotchkiss, E. R., Vasconcelos, F. R., Karlsson, J. & Byström, P. (2015). Climate change modifies the size structure of assemblages of emerging aquatic insects. Freshwater Biology, 60(1), 78-88
Open this publication in new window or tab >>Climate change modifies the size structure of assemblages of emerging aquatic insects
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2015 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, p. 78-88Article in journal (Refereed) Published
Abstract [en]

Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large-scale outdoor pond facility where 16 sections - each containing natural food webs including a fish top-consumer population - were subjected to warming (3 degrees C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming-induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2015
Keywords
aquatic subsidies, brownification, dissolved organic matter, pond ecosystems, warming
National Category
Oceanography, Hydrology and Water Resources Ecology Climate Research
Identifiers
urn:nbn:se:umu:diva-97882 (URN)10.1111/fwb.12468 (DOI)000346069800006 ()
Available from: 2015-01-16 Created: 2015-01-08 Last updated: 2018-06-07Bibliographically approved
Burrows, R. M., Hotchkiss, E. R., Jonsson, M., Laudon, H., McKie, B. G. & Sponseller, R. A. (2015). Nitrogen limitation of heterotrophic biofilms in boreal streams. Freshwater Biology, 60(7), 1237-1251
Open this publication in new window or tab >>Nitrogen limitation of heterotrophic biofilms in boreal streams
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2015 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 7, p. 1237-1251Article in journal (Refereed) Published
Abstract [en]

Nutrient limitation of the biofilm is fundamental to stream ecosystem processes, as microbial activity shapes the biological availability and biogeochemical cycling of carbon and nutrients. We used nutrient-diffusing substrata (NDS) to investigate heterotrophic nutrient limitation of microbial respiration (MR) across 20 streams draining boreal landscapes in northern Sweden. We also explored variation in microbial biomass and community structure of biofilms that developed on NDS using phospholipid fatty acid (PLFA) biomarkers. Limitation was determined as a significant response of MR and biomass production on cellulose surfaces to enrichment with nitrogen (N), phosphorus (P) or N+P, relative to controls. Microbial respiration was N-limited, with an average 3.3-fold increase on N-amended NDS. Nitrogen limitation decreased, and control rates of MR increased, with greater background concentrations of inorganic N across the sites. In contrast to MR, microbial biomass was primarily N-limited but was greatest for the N+P NDS. Accordingly, differences in respiratory versus biomass responses to nutrient addition resulted in significantly greater biomass-specific MR on N-amended NDS compared to all other treatments. In addition, PLFA biomarkers indicated distinct microbial communities on N and N+P NDS compared to controls and/or P NDS. Greater MR and biomass, and the development of distinct microbial communities, when supplied with inorganic N suggest that factors which alter aquatic N loading during autumn may have important implications for ecosystem processes and the biogeochemistry of boreal streams and rivers. Our findings add to a growing body of evidence that the productivity of Fennoscandian boreal landscapes is constrained by N availability.

Keywords
biofilms, microbial processing, nutrient limitation, phospholipid fatty acid, respiration
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-106316 (URN)10.1111/fwb.12549 (DOI)000356370800001 ()
Available from: 2015-07-17 Created: 2015-07-10 Last updated: 2018-06-07Bibliographically approved
Hotchkiss, E. & Hall, R. (2014). High rates of daytime respiration in three streams: Use of delta O-18(O2) and O-2 to model diel ecosystem metabolism. Limnology and Oceanography, 59(3), 798-810
Open this publication in new window or tab >>High rates of daytime respiration in three streams: Use of delta O-18(O2) and O-2 to model diel ecosystem metabolism
2014 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, no 3, p. 798-810Article in journal (Refereed) Published
Abstract [en]

Photosynthesis and respiration determine the carbon and oxygen (O-2) balance of ecosystems. Current methods used to estimate ecosystem respiration (ER) do not include diel ER fluctuations, which limit testing predictions about short-term drivers of ecosystem metabolism. Diel changes in delta O-18(O2) can be used to estimate diel ER due to discrimination against O-18(O2) during respiration. We monitored diel delta O-18(O2), O-2, light, and water temperature in three Wyoming streams and measured respiration fractionation (alpha(R)) against O-18(O2) in dark benthic flow chambers in two streams. The ranges of measured and literature alpha(R) values were used to estimate uncertainty in metabolism parameters associated with not measuring alpha(R) directly. Daytime ER was 54-340% higher than nighttime ER using delta O-18(O2), but diel ER parameter estimates were highly uncertain relative to traditional estimates of ecosystem metabolism. Diel variations in water temperature only accounted for 4-55% of the range of diel ER calculated using diel delta O-18(O2). Measured benthic flow chamber alpha(R) varied within the range of literature values: from 0.9755 to 0.9954. Metabolism parameter estimates were very sensitive to choice of alpha(R) within the measured and published range of values. The mean and uncertainty of diel ER estimates increased with decreasing alpha(R), with daily ER more than ten times higher given an alpha(R) of 0.975 vs. 0.999. Diel changes in ER can be modeled using delta O-18(O2) and O-2, but diel ER estimates depend on the choice of alpha(R), suggesting the need to better understand how alpha(R) may vary within spatial and temporal scales appropriate for delta O-18(O2) metabolism models.

National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-92679 (URN)10.4319/lo.2014.59.3.0798 (DOI)000339904300013 ()
Available from: 2014-09-02 Created: 2014-09-01 Last updated: 2018-06-07Bibliographically approved
Hotchkiss, E., Hall, R. O., Baker, M. A., Rosi-Marshall, E. J. & Tank, J. L. (2014). Modeling priming effects on microbial consumption of dissolved organic carbon in rivers. Journal of Geophysical Research - Biogeosciences, 119(5), 982-995
Open this publication in new window or tab >>Modeling priming effects on microbial consumption of dissolved organic carbon in rivers
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2014 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 119, no 5, p. 982-995Article in journal (Refereed) Published
Abstract [en]

Rivers receive and process large quantities of terrestrial dissolved organic carbon (DOC). Biologically available (unstable) DOC leached from primary producers may stimulate (i.e., prime) the consumption of more stable terrestrially derived DOC by heterotrophic microbes. We measured microbial DOC consumption (i.e., decay rates) from contrasting C sources in 10 rivers in the western and Midwestern United States using short-term bioassays of river water, soil and algal leachates, glucose, and commercial humate. We added inorganic nutrients (ammonium and phosphorus) to a subset of bioassays. We also amended a subset of river, soil, and commercial humate bioassays with glucose or algal leachates to test the hypothesis that unstable DOC primes consumption of more stable DOC. We used prior measurements of source-specific DOC bioavailability, linked with a Bayesian process model, to estimate means and posterior probability distributions for source-specific DOC decay rates in multisource bioassays. Modeled priming effects ranged from a -130 to +370% change in more stable DOC decay when incubated with unstable DOC. Glucose increased modeled river DOC decay by an average of 87% among all rivers. Glucose and algal leachates increased soil leachate and commercial humate decay by an average of 25% above background rates. Inorganic nutrient additions did not have consistent effects on DOC decay, likely because most of the study rivers had high ambient background nutrients. Our results demonstrate that the priming effect can augment DOC decay in rivers. In addition, Bayesian models can be used to estimate mechanisms driving aquatic ecosystem processes that are difficult to measure directly.

Keywords
rivers, carbon cycling, dissolved organic carbon, biological availability, priming effect, Bayesian inverse model
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:umu:diva-101043 (URN)10.1002/2013JG002599 (DOI)000337607900018 ()
Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2018-06-07Bibliographically approved
Hubbard, K. A., Lautz, L. K., Mitchell, M. J., Mayer, B. & Hotchkiss, E. R. (2010). Evaluating nitrate uptake in a Rocky Mountain stream using labelled N-15 and ambient nitrate chemistry. Hydrological Processes, 24(23), 3322-3336
Open this publication in new window or tab >>Evaluating nitrate uptake in a Rocky Mountain stream using labelled N-15 and ambient nitrate chemistry
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2010 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 24, no 23, p. 3322-3336Article in journal (Refereed) Published
Abstract [en]

Background aqueous chemistry and N-15(nitrate) tracer injection methods were used to calculate in-stream nitrate uptake metrics at Red Canyon Creek, a third-order stream in the Rocky Mountains in the state of Wyoming, United States. 'Net' nitrate uptake lengths, which reflect both nitrate uptake and regeneration, and 'gross' nitrate uptake lengths, which exclude re-mineralization, were quantified separately from background nitrate chemistry and N-15 labelling tracer data, respectively. Gross nitrate uptake lengths, from tracer injections of N-15 labelled nitrate, ranged from 502 to 3140 m. Net nitrate uptake lengths, from background nitrate chemistry downstream of a point source, ranged from 1170 to 4330 m. Diurnal changes in uptake lengths suggest the importance of nitrate utilization by autotrophs in the stream and benthic zone. The differences between net and gross nitrate uptake lengths along lower reaches of Red Canyon Creek allowed us to estimate the nitrate regeneration rate, which was 0.056-0.080 mu mol m(-2) s(-1) during the day and 0.0062-0.0083 mu mol m(-2) s(-1) at night. Spatial patterns of streambed pore water chemistry indicate those areas of the hyporheic zone where denitrification was likely occurring. Permanent log dams generated stronger redox gradients in the hyporheic zone than areas with transient beaver dams. By combining isotopically labelled nitrate additions, estimates of uptake from background aqueous nitrate chemistry and characterization of redox conditions in the hyporheic zone, we were able to determine the nitrate regeneration rate and the redox processes responsible for nitrogen cycling in the hyporheic zone. Copyright. (C) 2010 John Wiley & Sons, Ltd.

Keywords
nitrogen, uptake length, hyporheic zone, stable isotopes, tracer test, labelled N-15
Identifiers
urn:nbn:se:umu:diva-101044 (URN)10.1002/hyp.7764 (DOI)000284066600003 ()
Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2018-06-07
Hotchkiss, E. R. & Hall, R. O. (2010). Linking calcification by exotic snails to stream inorganic carbon cycling.. Oecologia, 163(1), 235-44
Open this publication in new window or tab >>Linking calcification by exotic snails to stream inorganic carbon cycling.
2010 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 163, no 1, p. 235-44Article in journal (Refereed) Published
Abstract [en]

Biotic calcification is rarely considered in freshwater C budgets, despite calculations suggesting that calcifying animals can alter inorganic C cycling. Most studies that have quantified biocalcification in aquatic ecosystems have not directly linked CO(2) fluxes from biocalcification with whole-ecosystem rates of inorganic C cycling. The freshwater snail, Melanoides tuberculata, has achieved a high abundance and 37.4 g biomass m(-2) after invading Kelly Warm Springs in Grand Teton National Park. This high biomass suggests that introduced populations of Melanoides may alter ecosystem processes. We measured Melanoides growth rates and biomass to calculate the production of biomass, shell mass, and CO(2). We compared Melanoides biomass and inorganic C production with ecosystem C pools and fluxes, as well as with published rates of CO(2) production by other calcifying organisms. Melanoides calcification in Kelly Warm Springs produced 12.1 mmol CO(2) m(-2) day(-1) during summer months. We measured high rates of gross primary productivity and respiration in Kelly Warm Springs (-378 and 533 mmol CO(2) m(-2) day(-1), respectively); CO(2) produced from biocalcification increased net CO(2) production in Kelly Warm Springs from 155 to 167 mmol CO(2) m(-2) day(-1). This rate of CO(2) production via biocalcification is within the published range of calcification by animals. But these CO(2) fluxes are small when compared to ecosystem C fluxes from stream metabolism. The influence of animals is relative to ecosystem processes, and should always be compared with ecosystem fluxes to quantify the importance of a specific animal in its environment.

Identifiers
urn:nbn:se:umu:diva-101045 (URN)10.1007/s00442-009-1536-1 (DOI)20058027 (PubMedID)
Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2018-06-07
Solomon, C. T., Hotchkiss, E. R., Moslemi, J. M., Ulseth, A. J., Stanley, E. H., Hall, R. O. . & Flecker, A. S. (2009). Sediment size and nutrients regulate denitrification in a tropical stream. Journal of The North American Benthological Society, 28(2), 480-490
Open this publication in new window or tab >>Sediment size and nutrients regulate denitrification in a tropical stream
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2009 (English)In: Journal of The North American Benthological Society, ISSN 0887-3593, E-ISSN 1937-237X, Vol. 28, no 2, p. 480-490Article in journal (Refereed) Published
Abstract [en]

Landuse changes might alter N cycling in tropical aquatic ecosystems, but understanding of N cycling in tropical streams is limited. We measured actual and potential denitrification rates during the dry season in Rio Las Marias, a 4(th)-order Andean piedmont stream in Venezuela. Our objectives were to describe spatial and temporal variation in denitrification, quantify the effects of nutrient availability and substratum particle size on denitrification, and explore potential effects of anthropogenic sedimentation on denitrification. In 4 experiments, actual and potential denitrification rates ranged from 0 to 160 and from 0 to 740 mu g N(2)O-N m(-2) h(-1), respectively. Rates were distributed approximately log-normally because of spatial variation. During a 1-mo period, actual denitrification rates decreased exponentially from 37 +/- 39 to 5 +/- 7 mu g N(2)O-N m(-2) h(-1) (mean +/- SD), probably because of a decline in water-column NO(3)-N concentration from 41 +/- 14 to 12 +/- 3 mu g NO(3)-N/L. The texture (particle size) of stream substrata markedly affected denitrification rates. Actual rates were low in cobble, gravel, and fine sediments (< 5 mm), but in fine sediments, rates increased in response to addition of excess NO(3)-N and organic C. In a 3-km stream reach, actual (but not potential) denitrification rates increased with the proportion of fine sediments (< 2 mm) in mixed substrata. This increase was nonlinear, and the threshold value occurred at 37% fine particles, above which actual denitrification rates were almost always high. An experiment simulating the effects of anthropogenic sedimentation showed that topsoil inputs resulted in denitrification rates similar to 8x higher than rates in trials where excess NO(3)-N and organic C were supplied. Denitrification is a small but potentially significant sink for available N in this N-limited system. Anthropogenic sedimentation associated with landuse change might significantly increase denitrification rates in streams.

Keywords
denitrification, stream, nitrogen cycle, tropics, anthropogenic sedimentation, land use
Identifiers
urn:nbn:se:umu:diva-101046 (URN)10.1899/07-157.1 (DOI)000266645700019 ()
Available from: 2015-03-18 Created: 2015-03-18 Last updated: 2018-06-07
Byström, P., Hedström, P., Hotchkiss, E., Rodríguez, P., Vasconcelos, R. F. & Karlsson, J.Warming decrease fish population densities and biomass.
Open this publication in new window or tab >>Warming decrease fish population densities and biomass
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Temperature impact all biota and ecosystems through its direct effect on the vital rates of primary producers and consumers. Still, how these changes in rates translates through ecosystem feed backs to the population level of top consumers are poorly understood. Here, we studied effects of temperature increase (+ 3 ̊C during ice free season) on fish population dynamics in a replicated large scale pond ecosystem experiment over 3 years. Increased temperature had no significant effect on whole ecosystem gross primary production while top down effects of warming on intermediate consumers changed from negative to positive due to negative effects of warming on fish population abundance. Total fish density and biomass and abundance of both mature and old fish decreased with warming, while proportion of young fish increased, with warming. The effects of warming on fish population demographics were likely due to that temperature increased cohort competition and fish energy requirements relative to resource production. Our results suggest that global warming may increase competition, favor young individuals and overall decrease fish population densities and biomass. 

National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-127936 (URN)
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2018-06-09
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