Article

Whole-stream metabolism in two montane streams: Contribution of the hyporheic zone

Limnology and Oceanography (Impact Factor: 3.62). 01/2001; 46(3). DOI: 10.4319/lo.2001.46.3.0523
Source: OAI

ABSTRACT We used whole-stream and benthic chamber methods to measure rates of metabolism and determine the contribution of the hyporheic zone to ecosystem respiration (R) in two streams with differing surface–subsurface exchange characteristics, Rio Calaveras and Gallina Creek, New Mexico. We used the difference between whole-stream and benthic R to calculate the rate of hyporheic zone R and coupled this estimate to an independent measure of hyporheic sediment R to estimate the cross-sectional area of the hyporheic zone (AH) for two reaches from each stream. Conservative tracer injections and solute transport modeling were used to characterize surface–subsurface hydrologic exchange by determining values of the cross-sectional area of the transient storage zone (As). The hyporheic zone contributed a substantial proportion of whole-stream R in all four study reaches, ranging from 40 to 93%. Wholestream R, hyporheic R, and percent contribution of hyporheic R all increased as transient storage increased, with whole-stream and hyporheic R exhibiting significant relationships with As. All three measures of respiration and values of AH were much greater for both reaches of the stream with greater surface–subsurface exchange. AH is valuable for cross-site comparisons because it accounts for differences in rates of both benthic and hyporheic sediment R and can be used to predict the importance of the hyporheic zone to other stream ecosystem processes. Yes Yes

Full-text

Available from: Clifford N Dahm, May 29, 2015
1 Follower
 · 
125 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: River regulation and altered land use are two common anthropogenic disturbances in rivers worldwide. Alteration of the stream bed, through processes such as siltation, or of hydrology through river regulation, are likely to modify hyporheic processes or clog interstitial space and thereby affect both hyporheic invertebrates and nutrient dynamics.We tested the separate and combined effects of increased flow and increased fine sediment on hyporheic water quality and invertebrates in flume mesocosms. Each mesocosm contained two bed sediment types: clean sediment in the upstream section and experimentally colmated (EC) sediment (10% by weight of fine sediment) in the downstream section. Two flow rates were established, a higher flow rate to create turbulent flow in six mesocosms and a lower flow rate to create a transitional flow between turbulent and laminar flows in the remaining six mesocosms. Invertebrates and physicochemistry were sampled after 30 days at three depths (5, 11 and 18 cm), and the flows in six of twelve mesocosms were switched. The experiment was concluded after sampling invertebrates and physicochemistry on day 70.The addition of fine sediment to the mesocosm bed generally increased ammonium and decreased nitrate and soluble reactive phosphorus concentrations, decreased oxygen penetration and altered invertebrate assemblage structure. Increased flow rates generally lowered ammonium concentrations, increased soluble reactive phosphorus concentrations, increased oxygen penetration and altered invertebrate assemblage structure. Our hypothesis that higher flows would ameliorate any effects of added fine sediment was generally supported for oxygen penetration and nitrate concentration. However, we observed no differences in interaction effects of flow regime and sediment type either on other nutrient concentrations or invertebrate assemblage structure.The rates of flow used in our mesocosms did not appear to reach the threshold required to remove fine sediment. It is generally recognised that river hyporheic restoration requires a set of objectives against which the outcomes can be measured yet this is often overlooked. Our research provides preliminary guidelines that small amounts of fine sediment can have deleterious ecological effects. However, further research is required to evaluate whether lower percentages of bed fine sediment result in ecological impairment and to determine what flow rates are required to ameliorate colmation impacts.
    Freshwater Biology 04/2015; 60(4). DOI:10.1111/fwb.12536 · 2.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated changes in respiration across night and daytime in a headwater stream. For this, we conducted consecutive nighttime and daytime experiments injecting the bioreactive tracer resazurin in two reaches with different riparian canopy densities (different levels of photosynthetically active radiation) to compare respiration rate coefficients. We found that even though stream water temperature measured above the streambed at day and night (half-day timescale) were different within each reach and across reaches (95% confidence level), apparent respiration rate coefficients were not different across nighttime and daytime conditions (95% confidence level). A likely explanation for this is that the bulk of stream respiration takes place in the hyporheic zone, where diel fluctuations of stream temperature and PAR are considerably attenuated (e.g., Constantz (2008)), and where temperature is not measured in routine investigations of stream metabolism. Our results suggest that community respiration in headwater streams may not need to be “corrected” for temperature between daytime and nighttime, even though instantaneous changes in respiration are expected to occur from a pure biological perspective.
    Ecohydrology 02/2015; DOI:10.1002/eco.1615 · 2.63 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inland waters are an important component of the global carbon cycle through transport, storage, and direct emissions of CO2 and CH4 to the atmosphere. Despite predictions of high physical gas exchange rates due to turbulent flows and ubiquitous supersaturation of CO2—and perhaps also CH4—patterns of gas emissions are essentially undocumented for high mountain ecosystems. Much like other headwater networks around the globe, we found that high-elevation streams in Rocky Mountain National Park, U.S.A. were supersaturated with CO2 during the growing season and were net sources to the atmosphere. CO2 concentrations in lakes, on the other hand, tended to be less than atmospheric equilibrium during the open water season. CO2 and CH4 emissions from the aquatic conduit were relatively small compared to many parts of the globe. Irrespective of the physical template for high gas exchange (high k), we found evidence of CO2 source limitation to mountain streams during the growing season, which limits overall CO2 emissions. Our results suggest a reduced importance of aquatic ecosystems for carbon cycling in high-elevation landscapes having limited soil development and high CO2 consumption via mineral weathering.
    Journal of Geophysical Research: Biogeosciences 05/2015; DOI:10.1002/2014JG002861 · 3.44 Impact Factor