Sensitivity of freshwaters to browning in response to future climate change

Abstract

Many boreal waters are currently becoming browner with effects on biodiversity, fish production, biogeochemical processes and drinking water quality. The question arises whether and at which speed this browning will continue under future climate change. To answer the question we predicted the absorbance (a 420 ) in 6347 lakes and streams of the boreal region under future climate change. For the prediction we modified a numerical model for a 420 spatial variation which we tested on a temporal scale by simulating a 420 inter-annual variation in 48 out of the 6347 Swedish waters. We observed that inter-annual a 420 variation is strongly driven by precipitation that controls the water flushing through the landscape. Using the predicted worst case climate scenario for Sweden until 2030, i.e., a 32 % precipitation increase, and assuming a 10 % increase in imports of colored substances into headwaters but no change in land-cover, we predict that a 420 in the 6347 lakes and streams will, in the worst case, increase by factors between 1.1 and 7.6 with a median of 1.3. This increase implies that a 420 will rise from the present 0.1-86 m −1 (median: 7.3 m ), which can cause problems for the preparation of drinking water in a variety of waters. Our model approach clearly demonstrates that a homogenous precipitation increase results in very heterogeneous a 420 changes, where lakes with a long-term mean landscape water retention time between 1 and 3 years are particularly vulnerable to climate change induced browning. Since these lake types are quite often used as drinking water resources, preparedness is needed for such waters.

Primary producers or consumers? Increasing phytoplankton bacterivory along a gradient of lake warming and browning

“…The five climate change treatments therefore ranged from a modest scenario with 1°C warming and 50% increase in absorbance to the most extreme scenario of 5°C warming and 250% increase in absorbance relative to the control. This latter scenario represents the upper range of warming predictions made by the IPCC‐reports, but implies rates of change over the coming century that are well below the fastest rates currently observed for both lake temperature (O'Reilly et al ) and browning (Weyhenmeyer et al ).…”

No long‐term trends in pCO2 despite increasing organic carbon concentrations in boreal lakes, streams, and rivers

“…Likewise, Weyhenmeyer et al [] showed that direct inputs of DIC from the terrestrial surroundings of a lake have a stronger influence on CO 2 concentrations in lake water than do lake internal CO 2 production. As precipitation and runoff have shown an overall increase across Sweden over the past few decades, in particular during the 1990s and 2000s [ Bengtsson and Rana , ; Lindström and Bergström , ; Weyhenmeyer et al ., , ], we suggest that most waters now receive proportionally more shallow groundwater compared to deep groundwater [ Laudon et al ., ] (Figure ). Such an increase most likely results in a DOC concentration increase in surface waters as DOC concentration in soil profiles tends to increase toward the top soil layers [ Grabs et al ., ; Kaiser and Kalbitz , ].…”

Phytoplankton diversity loss along a gradient of future warming and brownification in freshwater mesocosms

“…Mesocosm experiments provide a strong predictive basis for assessing the direction and strength of responses to ongoing environmental changes (Jeppesen et al., 2012; Spivak, Vanni, & Mette, ; Stewart et al., ). Our experiment captures the seasonal community changes under a predicted gradient of climate warming and brownification conditions in northern temperate lakes (IPCC, ; Monteith et al., ; Weyhenmeyer et al., ). However, it is important to stress that scaling up results to future climate change scenarios for the next decades should be done with caution (Stewart et al., ).…”

“…These warming conditions followed temperature projections from the Intergovernmental Panel on Climate Change for this century (IPCC, ). Our brownification scenarios were based on historical trends from southern Swedish lakes (Hansson et al., ), which lie within the range of the future projected increase in brownification for Swedish lakes (Weyhenmeyer et al., ).…”