Influence of the Landscape Template on Chemical and Physical Habitat for Brown Trout Within a Boreal Stream Network

We used the distribution of stream-dwelling brown trout (Salmo trutta) in a 67 km2 boreal catchment to explore the importance of environmental organizing factors at a range of spatial scales, including whole-catchment characteristics derived from map data, and stream reach chemical and physical characteristics. Brown trout were not observed at any sites characterized by pH < 5.0 during the spring snowmelt episode, matching published toxicity thresholds. Brown trout distributions were patchy even in less acidic regions of the stream network, positively associated with glaciofluvial substrate and negatively associated with fine sand/silty sediments. A multivariate model including only whole-catchment characteristics explained 43% of the variation in brown trout densities, while models with local site physical habitat characteristics or local stream chemistry explained 33 and 25%, respectively. At the stream reach scale, physical habitat apparently played a primary role in organizing brown trout distributions in this stream network, with acidity placing an additional restriction by excluding brown trout from acidic headwater streams. Much of the strength of the catchment characteristics-fish association could be explained by the correlation of catchment-scale landscape characteristics with local stream chemistry and site physical characteristics. These results, consistent with the concept of multiple hierarchical environmental filters regulating the distribution of this fish species, underline the importance of considering a range of spatial scales and both physical and chemical environments when attempting to manage or restore streams for brown trout.

Effects of Wildfires and Ash Leaching on Stream Chemistry in the Santa Ynez Mountains of Southern California

Wildfires can change ecosystems by altering solutes in streams. We examined major cations in streams draining a chaparral-dominated watershed in the Santa Ynez Mountains (California, USA) following a wildfire that burned 75 km2 from July 8 to October 5, 2017. We identified changes in solute concentrations, and postulated a relation between these changes and ash leached by rainwater following the wildfire. Collectively, K+ leached from ash samples exceeded that of all other major cations combined. After the wildfire, the concentrations of all major cations increased in stream water sampled near the fire perimeter following the first storm of the season: K+ increased 12-fold, Na+ and Ca2+ increased 1.4-fold, and Mg2+ increased 1.6-fold. Our results suggested that the 12-fold increase in K+ in stream water resulted from K+ leached from ash in the fire scar. Both C and N were measured in the ash samples. The low N content of the ash indicated either high volatilization of N relative to C occurred, or burned material contained less N.

Long-Term Concentrations and Loads of Four Dissolved Macronutrients from Two Agroforestry Catchments in NW Spain

Understanding hydrological processes controlling stream chemistry and quantifying solute concentrations over time is crucial for estimating future alterations of water quality due to land use or climate change impacts, as well as for setting preventive or remedial actions. In the current study, soluble sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) concentrations and loads were assessed in waters from two small catchments located at different distances to the sea (9 km Valiñas and 30 km Abelar) in NW Spain from 2003 to 2016. Solute concentrations were determined using spectrometric techniques, while streamflow data were employed for estimating loads. Moreover, concentration-discharge relations were calculated for each solute and catchment. The average concentrations of soluble Na+, K+, Ca2+ and Mg2+ were, respectively, 16.5, 2.6, 7.9 and 4.1 mg L−1 in Valiñas, and 8.2, 0.9, 2.9 and 3.4 mg L−1 in Abelar, although variability among samplings was high. The four soluble ions showed a dilution pattern in Valiñas, whereas in Abelar Na+ tended to a chemostatic behavior and K+ and Ca2+ were positively related to streamflow. In conclusion, the dominant processes controlling these relationships are local and depend on catchment characteristics such as land use (including slurry applications in Abelar), distance to the sea, and vegetation cover.