Emma Gibson1, Valérie Ouellet2, Nathan Watson3, Melinda D. Daniels2 1Missouri State University, Springfield, MO 2Stroud Water R
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Geomorphic and hydraulic controls on thermal regimes in stream pool habitats Emma Gibson1, Valérie Ouellet2, Nathan Watson3, Melinda D. Daniels2 1Missouri State University, Springfield, MO 2Stroud Water Research Center, Avondale, PA 3Cornell University, Ithaca, NY Results Introduction A significant difference in thermal regimes was seen between pools located in Stream pools provide important habitat to diverse communities of the three different reaches of the stream. The meadow, restoration forest, and macroinvertebrates and fish. In the summer, pools serve as vital cold-water mature forest each had distinct temperature patterns. Many of the refuges for fish and their prey, both of which have distinct thermal tolerance environmental parameters studied were correlated to different stream reaches. ranges (Torgersen et al. 2012). Some aspects of stream thermal regimes, like No significant correlation was found relating sediment size to stream reach. the cooling effect of riparian zones, water temperature modeling, spatial and The two pools with the most dissimilar thermal regimes in the restoration forest temporal water temperature variation, and the potential effects of climate and the mature forest were Pool 8 and Pool 10 respectively. Pool 8’s thermal change on stream temperature and habitat, have been well studied (Caissie regime is more closely related to air temperature than that of Pool 10. Thermal 2010, Fullerton et al. 2015, Garner et al. 2014, Isaak et al. 2012). Much stratification is more pronounced in Pool 10. Pool 10 is much deeper than Pool research still needs to be done to assess the effect that a stream’s physical 8. Pool 10 is located in a meander, while Pool 8 is forced in a straight section of characteristics have on its water temperature. This study addresses the need channel by several pieces of large woody debris. for a better understanding of geomorphic and hydraulic influence on thermal regimes in important stream pool habitats. Specifically this study asks: (1) How does pool depth affect water temperature? (2) How do flow 1.0 50 velocities affect water temperature? (3) Do sediment characteristics Maximum daily water temperature Relationships between environmental 0.8 40 relate to water temperature? (4) Is thermal stratification a distinct per pool parameters (NMDS results) 0.6 30 characteristic of stream pool thermal regimes ? 0.4 20 Depth Depth 0.2 D50 (mm) Average 10 0.0 0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 Study Area Pool Number Pools 10.00000 0.06 0.05 8.00000 0.04 6.00000 0.03 0.02 4.00000 Flow (VelXAvg) m/s Flow (VelXAvg) This study includes 10 pools in White 0.01 2.00000 Clay Creek, a headwater stream in 0.00 0.00000 Chester County, PA. The pools were Content of Sediment Organic Matter Percentage Average P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 located in three distinct reaches and Pools Pools were a representative sampling of the Geomorphic and hydraulic parameters by pool many types of pool habitats in the creek. Five of the studied pools are located in an open meadow, three are in an established restoration Conclusions forest (35 years), and two are in a mature forest (80-90 years). Water temperature at Pool 8 and Pool 10 • Riparian zones have a significant cooling impact on stream habitats and air temperature • Thermal stratification was not a significant factor in the thermal regimes of the studied pools. As stratification was seen in the deepest pool, there may be a depth threshold that must be reached for stratification to occur • No correlation between sediment grain size and temperature was found; Pool 8 Pool 10 however, sediments with higher organic matter contents were found in the cooler pools of the mature forest Top Bottom LWD Top Bottom LWD • Deeper pools and pools with large depth variability tend to be cooler • Flow velocity was positively correlated with the meadow pools which had R² 0.738859 0.74162639 0.69423302 0.525616 0.47401498 0.51623983 higher max temperatures and greater temperature variation than the forest Methods pools • Further study is needed to account for variability in temperature between Temperature: Stacks of shielded Onset HOBO V2 Pro water temperature R² values of data from each logger in Pool 8 and Pool 10 compared to air temperature pools loggers were used to measure temperature in the pools at 15 minute intervals • Moving forward, pool hydraulics will be analyzed spatially and PAR will be over a multi-week summer heat stress period. measured at each site Grain Size: Sediment samples were taken in each microhabitat patch in the pool and analyzed for grain size through dry sieving. Where appropriate, Wolman pebble counts were taken in the field. Organic Matter: Loss on ignition was used to test subsamples of homogenized Acknowledgements and References sediment samples • Caissie D. (2006) The thermal regime of rivers: a review. Freshwater Biology 51: 1389-1406. Topography: Pool topography was recorded using total station surveying. • Fullerton A. (2015) Rethinking the longitudinal stream temperature paradigm: region-wide comparison of thermal infrared imagery reveals unexpected complexity of river temperatures. Hydrological Processes DOI: Hydraulics: A SonTek handheld acoustic Doppler velocimeter was used to 10.1002/hyp.10506 measure flow velocity at equally spaced grid points throughout each pool. • Garner G. et al. (2014) What causes cooling water temperature gradients in a forested stream reach?. Hydrol. Earth Syst. Sci. 18:5361-5376. Statistical Analysis: Environmental variables were examined using Non Metric • Isaak D.J. et al. (2012) Climate change effects on stream and river temperatures across the northwest U.S. MultiDimensional Scaling (NMDS). Spearman rank correlation was used to from 1980-2009 and implications on salmonid fishes. Climatic Change 113:499-524 assess which specific environmental variables were related to a particular NMDS • Torgersen C. et al. (2012) Primer for Identifying Cold-Water Refuges to Protect and Restore Thermal Diversity in Riverine Landscapes. EPA 910-C-12-001. output. A significance cutoff of α = 0.20 was used to assess meaningful relationships between NMDS dimension scores and environmental data values. • Funding for this project was received from NSF EAR 1263212, a project entitled “Collaborative Research: REU/RET site - Introducing Critical Zone Observatory science to students and teachers” • I would like to acknowledge Jennie Matkov for all of her assistance in the field and Charlie Dow for his help with statistical analysis Looking downstream at Pool 8 (left) and Pool 10 .