Afforestation driving long‐term surface water browning

Abstract

Increase in surface water color (browning), caused by rising dissolved organic carbon (DOC) and iron concentrations, has been widely reported and studied in the last couple of decades. This phenomenon has implications to aquatic ecosystem function and biogeochemical carbon cycling. While recovery from acidification and changes in climate‐related variables, such as precipitation and length of growing season, are recognized as drivers behind browning, land‐use change has received less attention. In this study, we include all of the above factors and aim to discern their individual and combined contribution to water color variation in an unprecedentedly long (1940–2016) and highly resolved dataset (~20 times per month), from a river in southern Sweden. Water color showed high seasonal variability and a marked long‐term increase, particularly in the latter half of the dataset (~1980). Short‐term and seasonal variations were best explained by precipitation, with temperature playing a secondary role. All explanatory variables (precipitation, temperature, S deposition, and land‐use change) contributed significantly and together predicted 75% of the long‐term variation in water color. Long‐term change was best explained by a pronounced increase in Norway spruce (Picea abies Karst) volume—a measure of land‐use change and a proxy for buildup of organic soil layers—and by change in atmospheric S deposition. When modeling water color with a combination of explanatory variables, Norway spruce showed the highest contribution to explaining long‐term variability. This study highlights the importance of considering land‐use change as a factor behind browning and combining multiple factors when making predictions in water color and DOC.

Landscape controls on riverine export of dissolved organic carbon from Great Britain

“…R 2 = 0.46, P = 0.000001 planting to lower the water table sufficiently to allow conifers to grow. This observation is consistent with previous work suggesting that drained and afforested peatlands tend to have elevated DOC export (Evans et al 2016;Menberu et al 2017;Skerlep et al 2019) and with a recent targeted study of forested versus unforested blanket bogs in Northern Scotland (Pickard et al in prep.). The mapped spatial distribution of the DOC yields across GB reflects this land-use influence, with the highest yields observed from the afforested Fig.…”

Phosphorus Availability Promotes Bacterial DOC-Mineralization, but Not Cumulative CO2-Production

“…The DOC sustaining heterotrophic bacterial metabolism in aquatic ecosystems originates either from primary production within the system (autochthonous DOC) or from terrestrial primary production in the catchment (allochthonous DOC). There is a current trend of increasing transport of terrestrial DOC, to some extent also of total phosphorus (TP) and total nitrogen (TN), to inland waters, caused by factors such as recovery from acidification, climate change, and land use change (Monteith et al, 2007;Kellerman et al, 2015;Finstad et al, 2016;Kritzberg, 2017;Škerlep et al, 2020).…”

Negative effect of turbidity on prey capture for both visual and non‐visual aquatic predators

“…Despite these methodological differences, understanding the influence of turbidity range variation is relevant to known which species can cope well with reduced water transparency and which species are more prone to be locally extinct in a scenario of increased human‐induced changes in turbidity. Aquatic environments are experiencing a reduction in water clarity via multiple stressors, including eutrophication and climate change (Asknes et al, 2009; Meyer‐Jacob et al., 2020; Škerlep, Steiner, Axelsson, & Kritzberg, 2020). Thus, considering the body of evidence summarized here, an increase in turbidity may reduce the effects of predation on prey populations.…”