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1. Drying, more than warming, alters ecosystem functioning in streams with different energy pathways

   https://doi.org/10.1111/1365-2435.14351  

   Nelson, Daniel ; Busch, Michelle H. ; Kopp, Darin A. ; Allen, Daniel C. ( May 2023 , Functional Ecology)

   Empirical evidence and theory suggest that climate warming and an increase in the frequency and duration of drying events will alter the metabolic balance of freshwater ecosystems. However, the impacts of climate change on ecosystem metabolism may depend on whether energy inputs are of autochthonous or allochthonous origin. To date, few studies have examined how warming and drying may interact to alter stream metabolism, much less how their impacts may depend on the energy‐base of the food web.

   To address this research gap, we conducted a multi‐factorial experiment using outdoor mesocosms to investigate the individual and synergistic effects of warming and drought on metabolic processes in stream mesocosms with green (algal‐based) vs. mixed (algal‐ and detritus‐based) vs. brown (detritus‐based) energy pathways.

   We set up 48 mesocosms with one of three different levels of shade and leaf litter input combinations to create mesocosms with different primary energy channels. In addition, we warmed half of the mesocosms by ~2–3°C. We assessed changes in ecosystem respiration (ER), gross primary production (GPP), net ecosystem production (NEP) and organic matter biomass in warmed and ambient temperature mesocosms before a 24 day drying event and after rewetting.

   Surprisingly, experimental warming had little effect on metabolic processes. Drying, however, led to decreased rates of ER and GPP and led to an overall reduction in NEP. Although the effects of drying were similar across energy channel treatments, reductions in ER and GPP were primarily driven by decreases in biomass of benthic and filamentous algae.

   Overall, we demonstrate that drying led to lower rates of NEP in mesocosms regardless of energy inputs. While warming showed little effect in our study, our results suggest that an increase in the frequency of stream drying events could greatly alter the metabolic balance of many aquatic ecosystems.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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2. Stream metabolism sources a large fraction of carbon dioxide to the atmosphere in two hydrologically contrasting headwater streams

   https://doi.org/10.1002/lno.12226  

   Bernal, Susana ; Cohen, Mathew J. ; Ledesma, José L. J. ; Kirk, Lily ; Martí, Eugènia ; Lupon, Anna ( September 2022 , Limnology and Oceanography)

   Headwater streams are control points for carbon dioxide (CO₂) emissions to the atmosphere, with relative contributions to CO₂emission fluxes from lateral groundwater inputs widely assumed to overwhelm those from in‐stream metabolic processes. We analyzed continuous measurements of stream dissolved CO₂and oxygen (O₂) concentrations during spring and early summer in two Mediterranean headwater streams from which we evaluated the contribution of in‐stream net ecosystem production (NEP) to CO₂emission. The two streams exhibited contrasting hydrological regimes: one was non‐perennial with relatively small groundwater inflows, while the other was perennial and received significant lateral groundwater inputs. The non‐perennial stream exhibited strong inverse coupling between instantaneous and daily CO₂and O₂concentrations, and a strong correlation between aerobic ecosystem respiration (ER) and gross primary production (GPP) despite persistent negative NEP. At the perennial stream, the CO₂–O₂relationship varied largely over time, ER and GPP were uncorrelated, and NEP, which was consistently negative, increased with increasing temperature. Mean NEP contribution to CO₂emission was 51% and 57% at the non‐perennial and perennial stream, respectively. Although these proportions varied with assumptions about metabolic stoichiometry and groundwater CO₂concentration, in‐stream CO₂production consistently and substantially contributed to total atmospheric CO₂flux in both streams. We conclude that in‐stream metabolism can be more important for driving C cycling in some headwater streams than previously assumed.

    

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3. Response of lake metabolism to catchment inputs inferred using high‐frequency lake and stream data from across the northern hemisphere

   https://doi.org/10.1002/lno.12449  

   Corman, Jessica R. ; Zwart, Jacob A. ; Klug, Jennifer ; Bruesewitz, Denise A. ; de Eyto, Elvira ; Klaus, Marcus ; Knoll, Lesley B. ; Rusak, James A. ; Vanni, Michael J. ; Alfonso, María Belén ; et al ( November 2023 , Limnology and Oceanography)

   In lakes, the rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) are often controlled by resource availability. Herein, we explore how catchment vs. within lake predictors of metabolism compare using data from 16 lakes spanning 39°N to 64°N, a range of inflowing streams, and trophic status. For each lake, we combined stream loads of dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) with lake DOC, TN, and TP concentrations and high frequencyin situmonitoring of dissolved oxygen. We found that stream load stoichiometry indicated lake stoichiometry for C : N and C : P (r² = 0.74 andr² = 0.84, respectively), but not for N : P (r² = 0.04). As we found a strong positive correlation between TN and TP, we only used TP in our statistical models. For the catchment model, GPP and R were best predicted by DOC load, TP load, and load N : P (R² = 0.85 andR² = 0.82, respectively). For the lake model, GPP and R were best predicted by TP concentrations (R² = 0.86 andR² = 0.67, respectively). The inclusion of N : P in the catchment model, but not the lake model, suggests that both N and P regulate metabolism and that organisms may be responding more strongly to catchment inputs than lake resources. Our models predicted NEP poorly, though it is unclear why. Overall, our work stresses the importance of characterizing lake catchment loads to predict metabolic rates, a result that may be particularly important in catchments experiencing changing hydrologic regimes related to global environmental change.

    

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4. High-frequency dissolved oxygen, water temperature, wind speed, and radiation data; stream and in-lake nutrient concentration data; and daily metabolism and nutrient loading estimates for 16 lakes in North America and Northern Europe.

   https://doi.org/10.6073/pasta/ba8861853e02b19c9693cb100f722a02  

   Corman, Jessica ; Zwart, Jacob ; Klug, Jennifer ; Bruesewitz, Denise ; de Eyto, Elvira ; Klaus, Marcus ; Knoll, Lesley ; Rusak, James ; Vanni, Michael ; Alfonso, Maria Belen ; et al ( January 2023 , Environmental Data Initiative)

   In lakes, ecosystem structure and processes are influenced by gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP). The rates of these metabolic processes are often controlled by resource availability, which often reflects catchment loads. Although the relationship between catchment loads and in-lake nutrient concentrations may be well defined in specific lakes, we explored how watershed vs. in-lake predictors of metabolism compare across lake types. To do this, we combined stream loads of carbon (C), nitrogen (N), and phosphorus (P) with high frequency in situ monitoring of lake metabolism and in-lake C, N, and P concentrations from 16 lakes spanning a range of latitudes (39 to 64 degrees N), inflowing stream (0 - 6 streams), and trophic status (oligotrophic to eutrophic). The data package includes high-frequency dissolved oxygen, water temperature, wind speed, and solar radiation data as well as daily estimates of GPP, R, and NEP derived from those data. In addition, the data package includes in-lake and stream concentrations of dissolved organic carbon, total nitrogen, and total phosphorus and stream discharge data. The package also includes estimates of daily carbon, nitrogen and phosphorus loading to each lake derived from the stream concentrations and discharge. 

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5. The influence of lithology on stream metabolism in headwater systems

   https://doi.org/10.1002/eco.2284  

   Cargill, Samantha K. ; Segura, Catalina ; Villamizar, Sandra R. ; Warren, Dana R. ( February 2021 , Ecohydrology)

   Physical disturbances in streams have important effects on rates of gross primary production (GPP) and ecosystem respiration (ER). Underlying lithology can control sediment size, amount, and evolution in the stream, influencing substrate stability and in turn benthic organisms. We assessed patterns of disturbance and recovery for metabolic processes of GPP and ER associated with periods of increased flow and suspended sediment flux between December and April in two streams in the Oregon Coast Range with differing lithologies (basalt and sandstone). The results of whole‐stream metabolism modelling indicate that the two study streams have varying patterns of response and recovery rates after storm events. Both streams were heterotrophic during the entirety of the study period with changes in heterotrophy driven by changes in ER. Poststorm GPP decreased in both streams, but the basalt basin had greater proportional decreases and recovered slower than the sandstone basin. This result was unexpected and appeared to be associated with lower light availability in the basalt basin driven by increased turbidity during storm events; the coarser basalt substrate weathers into smaller size fractions than the finer sandstone substrate, remaining in suspension over longer periods and limiting light availability to benthic primary producers. The rates of ER in the sandstone basin did not change from prestorm to poststorm, whereas rates of ER in the basalt basin had varying responses. Overall, our results indicated that the underlying lithology of small mountain streams can drive variability in GPP by controlling sediment size and light availability during storms events.

    

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