Influence of Topography and Forestry on Catchments: Soil Properties, Runoff Regime, and Mercury Outputs

The dynamic development of terrestrial and aquatic environments in boreal catchments is controlled by the factors of parent material, climate, topography, biota, time, and anthropogenic activity. This thesis explores two of these factors, topography and the anthropogenic activity of forestry, as well as their control on the redistribution of solutes in the landscape. On a local scale for two undisturbed sites, the calculation of the topographical wetness index, TWI, was varied to better correlate to site properties. TWI values derived from large scale topographical features correlated better with soil pH and distribution of vascular plants (r=0.5-0.8), whereas a more locally derived TWI correlated better with soil moisture conditions (r=0.7-0.8). Even on a regional scale, the TWI correlated well with soil properties confirming its major control on soil evolution for the relatively young soils of the Swedish boreal zone. The disturbance of forest harvest in March 2006 according to best management practice was found to increase the annual flow by 35%, with a larger effect during the growing season (50-70%) than the dormant season (10-30%). Compared to other studies the change in concentration and export of mercury (Hg), methylmercury (MeHg), and total organic carbon (TOC) was minimal. During summer 2007 high frequency episode sampling, though, there was a significant increase in dissolved organic carbon (DOC) for the harvested sites compared to the reference sites. The results confirm that topography is a potential indicator for various site properties, such as soil chemistry, in the upland zone as well as the near stream zone. It is also a relatively neglected source of information that can be refined further. Forestry’s impact on the mercury load to the aquatic environment was found smaller in this study compared to other similar studies. This might be due to the thick snowpack that protected from soil impacts during harvest, as well as the fact that site preparation had not been conducted, and that the near stream zone was left intact.