Editing IPCC:AR6/WGII/Chapter-14 (section)

==== 14.5.1.2 Freshwater Ecosystems: Observed Impacts and Projected Risks ====

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Climate change, either directly (warming water) or indirectly (glacier and snow inputs), has affected biogeochemical cycling and species composition in North American aquatic ecosystems ( ''very high confidence'' ) (Table 14.2; [[#Moser--2005|Moser et al., 2005]] ; [[#Saros--2010|Saros et al., 2010]] ; [[#Preston--2016|Preston et al., 2016]] ), possibly amplifying other human-caused stresses on these systems ( [[#Richter--2016|Richter et al., 2016]] ). Excess nutrients associated with high farm animal density can be transported during intense rainfall events (expected to increase with climate change) causing algal blooms, fish kills and other detrimental ecological effects ( [[#Huisman--2017|Huisman et al., 2017]] ; [[#Coffey--2019|Coffey et al., 2019]] ).

Projected climate change will cause habitat loss, alter physical and biological processes, and decrease water quality in freshwater ecosystems ( ''high confidence'' ) ( [[#Poesch--2016|Poesch et al., 2016]] ; [[#Crozier--2019|Crozier et al., 2019]] ). Projected river warming of 1°C–3°C is expected to reduce thermal habitat for important salmon and trout species in the northwest USA by 5–31% ( [[#Isaak--2018|Isaak et al., 2018]] ) and in Mexico ( [[#Meza-Matty--2021|Meza-Matty et al., 2021]] ), and for multiple fish species in Canada ( [[#Poesch--2016|Poesch et al., 2016]] ). Cold-water streams at higher elevations will warm less and therefore may become climate refugia ( [[#Isaak--2016|Isaak et al., 2016]] ). Projected warming of mountain lake ecosystems ( [[#Roberts--2017b|Roberts et al., 2017b]] ; [[#Redmond--2018|Redmond, 2018]] ) will affect ecosystem processes ( [[#Preston--2016|Preston et al., 2016]] ; [[#Redmond--2018|Redmond, 2018]] ; [[#Moser--2019|Moser et al., 2019]] ). Loss of cold-water inputs from retreating glaciers are expected to adversely affect alpine stream ecosystems ( [[#Fell--2017|Fell et al., 2017]] ; [[#Giersch--2017|Giersch et al., 2017]] ). For anadromous fish species (e.g., Chinook salmon), future warming will reduce habitat suitability from river headwaters to oceans ( [[#Crozier--2021|Crozier et al., 2021]] ).

Freshwater ecosystems across North America are increasingly at risk from extreme drought, compounded by human demands for water ( [[#14.5.3|Section 14.5.3]] ; [[#Kovach--2019|Kovach et al., 2019]] ). Implications for aquatic and riparian species can vary, but it is widely agreed that these systems are highly sensitive to fluctuations in the hydrological cycle, which can increase competition by invasive species and compromise connectivity between potential cold-water refugia ( [[#Melis--2016|Melis et al., 2016]] ; [[#Poff--2019|Poff, 2019]] ).

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