Effects of different forest management options on water quality of inland waters

Summary

Globally, inland waters are at present delivering about 900 Million tons of Carbon (C) yr-1 to the oceans which is about 10% of the carbon C emissions from fossil fuels, and in addition, about 600 Million tons of C yr-1 are deposited as sediments in inland waters. Over the last years increasing dissolved organic matter (DOM) concentrations have been observed. This, so called, “Aquatic browning” has far-reaching consequences for ecology on a global scale, since it has major impacts on the global carbon C balance and water quality, but reasons for the observed brownification are still unclear (Hudson et al. 2003; Riise et al. 2012; Freeman et al. 2004). In the Nordic countries land use such as forest management practices (Kritzberg 2017) or drainage of peatlands also play an important role in increasing aquatic DOM concentration (Kortelainen and Saukkonen 1998; Nieminen 2004). Around 65% of the land area in Nordic countries is covered by forests of which up to 25% is on drained peatlands (Vasander et al. 2003). Ditch network maintenance (DNM) operations are needed to ensure the growth of trees on the otherwise waterlogged peat soils. However, this utilization of peatland forests causes additional pressure on water quality due to the risk of releasing large amounts of organic matter to freshwater ecosystems (O’Driscoll et al. 2018). Nutrients and organic matter transported in runoff and drainage water causes eutrophication which increases the oxygen consumption. Although the effects of brownification varies, it also often results in increased hypoxia and even anoxia.

brownification DOM Nordic countries