The boreal landscape is complex mosaic of vast forests, lakes and wetlands. Through the landscape flows a fine network of streams and rivers, carrying dissolved and suspended material from atmospheric deposition and weathering of soils and bedrock to downstream recipients. This thesis investigates the transport of U, Th and other metals in the boreal landscape by comparing a set of catchments with contrasting characteristics, ranging from 0.12-68 km2 in area. Using uranium (234U/238U) and oxygen isotopes (δ18O) it was demonstrated that catchment size has a strong impact on the hydrological pathways and on the mobilisation of uranium. Both tracers also displayed a consistent shift towards more superficial sources and more superficial flow pathways when going from winter baseflow conditions to the spring flood. Large spatiotemporal variability was observed with U fluxes ranging from 1.7 -30 g km-2 a-1. Using a wide set of hydrochemical parameters and landscape characteristics it was demonstrated that wetlands play a decisive role for the biogeochemical cycling of many metals. Comparing normalised fluxes of 13 different elements (Al, Ba, Ca, Cr, Cu, La, Mg, Na, Ni, Si, Sr, U and Y) 73% of the spatial variance could be explained based on the wetland coverage and the affinity for organic matter, the latter of which was quantified using thermodynamic modelling. Hence, it was possible to link the large-scale transport patterns of a wide range of metals to fundamental biogeochemical properties. When restraining the analysis to the smaller streams (<10 km2), the explanatory power increased to 88%. For elements such as Na and Si with low affinity for organic matter the decrease in wetland-dominated catchments corresponded closely to the area of mineral soils that had been replaced by peat, indicating that reduced weathering was the main cause of the decrease. For organophilic metals the decrease in wetland-dominated catchments was even greater, suggesting that there also was an accumulation of these metals in the peat. This was confirmed by investigating the distribution of radionuclides in local mire, which revealed considerable accumulation of uranium and thorium along the edges of the mire. Based on the inventories of uranium and thorium and their distribution in the peat it was concluded that the mire historically had been a sink for these metals and that it most likely will continue to be so for a long time to come. All and all, wetlands were estimated to decrease the fluxes of metals from the boreal forests to downstream lakes and oceans by 20-40%, depending on how strongly they bind to organic matter.

<p>Riparian vegetation along streams and rivers affects the aquatic community in numerous ways and often operates as a link for energy flux between forest and streams. The studies presented in this licentiate thesis focus on light and terrestrial invertebrates, two factors influenced by riparian zone structure, which potentially affect stream ecosystems and thus also brown trout (Salmo trutta). Paper I is a laboratory experiment where I study size dependent foraging behavior on surface-drifting terrestrial invertebrates and benthic invertebrates by brown trout. The results show a size-dependent difference in foraging ability with large trout being better able to use terrestrial surface prey than small trout. I argue that such ontogenetic foraging differences are due to both morphological constraints (eg. gape limitation) and size dependent behavioral differences related to predation risk. Paper II consists of a 5 month-long 2x2 factorial design field experiment where my objective was to examine the effects of terrestrial invertebrate input and solar radiation (PAR) on different trophic levels in a boreal headwater stream. More specifically, I followed the effects of increased light and decreased terrestrial invertebrate subsidies on periphyton, benthic macroinvertebrates and two size classes of the top fish predator, brown trout. The results showed that the reduction of terrestrial invertebrate input had size- and seasonal-dependent effects on trout, where large trout had lower growth rates than small trout, mainly in summer. Diet analyses of trout supported growth differences in that large trout in unmanipulated enclosures consumed relatively more terrestrial prey than large trout living in enclosures with reduced terrestrial inputs. A higher reliance on terrestrial prey subsidies by large trout compared to small may be explained by ontogenetic differences in foraging and habitat choice. Despite a 2.5-fold increase in PAR, light did not have an effect on chlorophyll a biomass, nor was there an effect on the density or composition of benthic macroinvertebrates. The lack of effects on primary production may be explained by very low nutrient levels in the stream.</p>

Riparian vegetation along streams and rivers affects the aquatic community in numerous ways and often operates as a link for energy flux between forest and streams. The studies presented in this licentiate thesis focus on light and terrestrial invertebrates, two factors influenced by riparian zone structure, which potentially affect stream ecosystems and thus also brown trout (Salmo trutta). Paper I is a laboratory experiment where I study size dependent foraging behavior on surface-drifting terrestrial invertebrates and benthic invertebrates by brown trout. The results show a size-dependent difference in foraging ability with large trout being better able to use terrestrial surface prey than small trout. I argue that such ontogenetic foraging differences are due to both morphological constraints (eg. gape limitation) and size dependent behavioral differences related to predation risk. Paper II consists of a 5 month-long 2x2 factorial design field experiment where my objective was to examine the effects of terrestrial invertebrate input and solar radiation (PAR) on different trophic levels in a boreal headwater stream. More specifically, I followed the effects of increased light and decreased terrestrial invertebrate subsidies on periphyton, benthic macroinvertebrates and two size classes of the top fish predator, brown trout. The results showed that the reduction of terrestrial invertebrate input had size- and seasonal-dependent effects on trout, where large trout had lower growth rates than small trout, mainly in summer. Diet analyses of trout supported growth differences in that large trout in unmanipulated enclosures consumed relatively more terrestrial prey than large trout living in enclosures with reduced terrestrial inputs. A higher reliance on terrestrial prey subsidies by large trout compared to small may be explained by ontogenetic differences in foraging and habitat choice. Despite a 2.5-fold increase in PAR, light did not have an effect on chlorophyll a biomass, nor was there an effect on the density or composition of benthic macroinvertebrates. The lack of effects on primary production may be explained by very low nutrient levels in the stream.

Thesis (Ph. D.)--University of Hong Kong, 1981.

Thesis (Ph.D.)--University of Hong Kong, 1981. / Also available in print.

Stream crossings are an integral component of forest road systems that provide access for timber harvesting and silvicultural activities. Stream crossings and their associated approaches are often the most critical point of concern for water quality along forest roads. Several types of crossings are used for extracting timber, but limited studies actually compare different types of stream crossings with regard to their effect on water quality. The objectives of this study were to examine four different stream crossing structures: 1) steel bridges, 2) pole bridges (pipe with poles), 3) standard culverts, and 4) re-enforced fords (with GeoWeb or Geotextile) to determine the influence of stream crossing type on water quality and to evaluate erosion associated with stream crossing approaches. We also evaluated each site at four different time intervals to determine if water quality was more affected during different stages of the operations. Prior to operational timber harvests, we identified six replications for each type of crossings (4 fords) and collected data at four time intervals: 1) prior to reopening or installation of crossing, 2) after crossing installation, 3) during harvest operation, and 4) after road closure. Potential erosion rates from approaches to the crossings were estimated by collecting the road/site information necessary to estimate erosion with the Water Erosion Prediction Project for forest roads (WEPP) and the forest version of the Universal Soil Loss Equation (USLE). In-stream water samples were collected at fixed locations above and below each crossing and were evaluated for total dissolved solids (TDS), pH, conductivity, water temperature, and total suspended solids (TSS) or sediment concentration. Steel bridge crossings generally caused the least amount of water quality disturbance. Model-generated estimates of erosion demonstrated that culvert crossings were associated with the highest average soil loss potential. Although steel bridge crossings had the best overall results, pole bridges proved to be a viable option for ephemeral or intermittent streams due to low potential of soil loss. Ford crossings were found to impact water quality indicators, but showed a decrease in total dissolved solids (TDS) after installation, prior to harvest. Overall, the steel skidder bridges were generally the best crossing type, but any of the crossings can be used effectively with minimal impact under specific site conditions and with judicious installation, use, and closure. Road/skid trail location and adherence to existing road grade, water control, cover, and closure best management practices are critical for protection of water quality at stream crossings. / Master of Science

<p>Det svenska skogsbruket har lett till minskade vedmängder i skogsbäckarna. Detta kan undvikas genom att orörda kantzoner lämnas. Kantzonsvegetatioen har även visats påverka nedfallet av terrestra evertebrater, vilket visats minska andelen terrestra evertebrater i laxfiskars diet. Ofta lämnas dock inga kantzoner. Vedmängden kan återställas genom ett vedtillskott. Ett vedtillskott leder till ökat antal och högre biomassa av laxfiskar och högre mängd bottenlevande evertebrater i de behandlade områdena. Nyligen nedsänkt ved koloniseras snabbt av evertebrater. I denna studie undersöktes effekterna av ett vedtillskott och reducerat evertebratnedfall på öringens (Salmo trutta) diet i ett fältexperiment i en skogsbäck, från juni till augusti 2007. Tillskottet av ved ledde till signifikant högre totalbiomassa i dieten i juli men inte i augusti Vedtillskottet ledde även till en lägre andel Dipteraadulter i dieten i juli. Reduktionen av evertebratnedfallet hade ingen påverkan på den totala andelen terrestra evertebrater i öringens diet. Reduktionen gav dock upphov till lägre Formicidae och Dipteraadult andel, i juli och lägre Formicidaebiomassa i dieten i juli. En kombination av ett vedtillskott och reducerat evertebratnedfall hade ingen påverkan på öringens diet. Slutsatserna var att den högre dietbiomassan vedtillskottet gav upphov till i juli, troligen berodde på en initial ökning i bytesförekomsten. Att andelen terrestra evertebrater i dieten inte minskade när evertebrat nedfallet reducerades berodde troligen på att reduktionen inte var tillräckligt stor för att ett dietskifte skulle ske. Frånvaron av signifikanta skillnader för behandlingen med både vedtillskott och reducerat nedfall berodde antagligen på att reduktionen i nedfallet motverkade effekten ett vedtillskott gav på dietbiomassan.</p> / <p>The Swedish forestry has caused a decrease in amounts of woody debris in the forest streams. This can be avoided by leaving an untouched riparian strip. A lack of riparian strip vegetation has also been shown to reduce the input of terrestrial invertebrates, which has been shown to reduce the proportion of terrestrial invertebrates in the diet of salmonides. In many cases such strips are not left. The amount of woody debris in a stream can be restored by a supplement of woody debris. That has been shown to lead to higher salmonide abundance and biomass and higher abundance of benthic invertebrates in the treated area. It has also been shown that newly submerged wood is rapidly colonised by invertebrates. In this study the effects of a supplement of woody debris and reduced input of terrestrial invertebrates on the diet of brown trout (Salmo trutta) was examined in a field experiment. The study took place with enclosures in a Swedish boreal stream, from June to August 2007. Introduction of woody debris caused a significantly higher diet biomass in July but not in August. The wood treatment also caused a decrease in the proportion of Diptera adults in the diet in July. The reduction of terrestrial invertebrate input didn’t affect the total proportion of terrestrial invertebrates in the trout diet. Nevertheless there was a significant decrease in the proportion and biomass of Formicidae and the proportion of Diptera adults in the diet in June. The combination of both treatments didn’t have any significant effect on the trout diet. The conclusions were that the higher diet biomass in July caused by woody debris addition, probably was due to an initial increase in the abundance of available aquatic invertebrates. The lack off effect from the reduced input of terrestrial invertebrate on the trout diet, was most likely due to the fact that the decrease in terrestrial invertebrate input probably wasn’t large enough to cause a dietary switch. The lack of effect of a combination of the two treatments indicated that the reduced input of terrestrial invertebrates cancelled out the effect of the added woody debris.</p>

Det svenska skogsbruket har lett till minskade vedmängder i skogsbäckarna. Detta kan undvikas genom att orörda kantzoner lämnas. Kantzonsvegetatioen har även visats påverka nedfallet av terrestra evertebrater, vilket visats minska andelen terrestra evertebrater i laxfiskars diet. Ofta lämnas dock inga kantzoner. Vedmängden kan återställas genom ett vedtillskott. Ett vedtillskott leder till ökat antal och högre biomassa av laxfiskar och högre mängd bottenlevande evertebrater i de behandlade områdena. Nyligen nedsänkt ved koloniseras snabbt av evertebrater. I denna studie undersöktes effekterna av ett vedtillskott och reducerat evertebratnedfall på öringens (Salmo trutta) diet i ett fältexperiment i en skogsbäck, från juni till augusti 2007. Tillskottet av ved ledde till signifikant högre totalbiomassa i dieten i juli men inte i augusti Vedtillskottet ledde även till en lägre andel Dipteraadulter i dieten i juli. Reduktionen av evertebratnedfallet hade ingen påverkan på den totala andelen terrestra evertebrater i öringens diet. Reduktionen gav dock upphov till lägre Formicidae och Dipteraadult andel, i juli och lägre Formicidaebiomassa i dieten i juli. En kombination av ett vedtillskott och reducerat evertebratnedfall hade ingen påverkan på öringens diet. Slutsatserna var att den högre dietbiomassan vedtillskottet gav upphov till i juli, troligen berodde på en initial ökning i bytesförekomsten. Att andelen terrestra evertebrater i dieten inte minskade när evertebrat nedfallet reducerades berodde troligen på att reduktionen inte var tillräckligt stor för att ett dietskifte skulle ske. Frånvaron av signifikanta skillnader för behandlingen med både vedtillskott och reducerat nedfall berodde antagligen på att reduktionen i nedfallet motverkade effekten ett vedtillskott gav på dietbiomassan. / The Swedish forestry has caused a decrease in amounts of woody debris in the forest streams. This can be avoided by leaving an untouched riparian strip. A lack of riparian strip vegetation has also been shown to reduce the input of terrestrial invertebrates, which has been shown to reduce the proportion of terrestrial invertebrates in the diet of salmonides. In many cases such strips are not left. The amount of woody debris in a stream can be restored by a supplement of woody debris. That has been shown to lead to higher salmonide abundance and biomass and higher abundance of benthic invertebrates in the treated area. It has also been shown that newly submerged wood is rapidly colonised by invertebrates. In this study the effects of a supplement of woody debris and reduced input of terrestrial invertebrates on the diet of brown trout (Salmo trutta) was examined in a field experiment. The study took place with enclosures in a Swedish boreal stream, from June to August 2007. Introduction of woody debris caused a significantly higher diet biomass in July but not in August. The wood treatment also caused a decrease in the proportion of Diptera adults in the diet in July. The reduction of terrestrial invertebrate input didn’t affect the total proportion of terrestrial invertebrates in the trout diet. Nevertheless there was a significant decrease in the proportion and biomass of Formicidae and the proportion of Diptera adults in the diet in June. The combination of both treatments didn’t have any significant effect on the trout diet. The conclusions were that the higher diet biomass in July caused by woody debris addition, probably was due to an initial increase in the abundance of available aquatic invertebrates. The lack off effect from the reduced input of terrestrial invertebrate on the trout diet, was most likely due to the fact that the decrease in terrestrial invertebrate input probably wasn’t large enough to cause a dietary switch. The lack of effect of a combination of the two treatments indicated that the reduced input of terrestrial invertebrates cancelled out the effect of the added woody debris.