Interactive effects of higher temperature and dissolved organic carbon on planktonic communities in fishless mountain lakes

Abstract

Summary We tested the hypothesis that higher temperature and dissolved organic carbon (DOC) concentration increase dissolved and particulate carbon (C) relative to phosphorus (P), thereby reducing algal food quality for P‐limited cladocerans while not affecting N‐limited copepods. Also, we expected alpine zooplankton to respond more strongly than those from warmer montane lakes to increased water temperature. Plankton from two alpine lakes and two montane lakes were incubated in vitro for 30 days at 10 or 17 °C and with ambient or +80% DOC, which was achieved by concentrating humic substances from each lake via reverse osmosis. Dissolved organic carbon amendments and warming significantly increase particulate C : P under montane, but not alpine conditions. While higher water temperature and DOC separately reduced phytoplankton abundance, together they increased phytoplankton by stimulating uptake of P. Warming stimulated only Daphnia while suppressing the abundance of the calanoid copepod Hesperodiaptomus when they originated from the three coldest lakes. Particulate C : P was positively correlated with Daphnia abundance and negatively correlated with Hesperodiaptomus, probably due to greater P‐retention by Daphnia. Our findings highlight the importance of interactions between the ecological effects of higher temperature and increased inputs of terrestrial organic matter to forecasts of the net impact of global warming on mountain lakes. Such predictions may be confounded if they are derived solely from the expected sum of single effects by each climatic factor.

Invasive trout increase the climatic sensitivity of zooplankton communities in naturally fishless lakes

“…Our discovery that non‐native trout enhance the effects of higher temperature on montane lake food webs adds to the growing evidence that interactions among stressors often produce unexpected net effects in the sensitive communities of mountain lakes (Thompson, Jacques & Vinebrooke, ; Weidman et al ., ). Further, the subtle direct effect of high temperature highlights the potential for forecasts of the effects of global warming to underestimate the actual outcome if the potential amplifying influences of other stressors are not considered.…”

“…However, the potential for non‐native trout and other environmental drivers (e.g. Weidman et al ., ) to synergistically increase the effects of warming on fishless mountain lakes suggests that indirect effects of global warming may be of much greater concern.…”

Alpine limnology of the Rocky Mountains of Canada and the USA in the context of environmental change

“…Moderate warming stimulates large daphniid species, but suppresses (Weidman et al 2014;Fischer et al 2011) or reduces reproduction (Thompson et al 2008)…”

“…Changes in water clarity would alter depth refugia and diurnal vertical migration processes of UV-sensitive zooplankton (Weidman et al 2014;Fischer et al 2015). However, warming may mitigate the effects of increased UV exposure in some taxa by increasing enzymatic photo-repair processes (Williamson et al 2002).…”

“…Alternatively, in some lakes, climate change may increase DOC in response to increased glacial ablation and treeline advancement, which could in turn increase productivity and diversity (Vinebrooke and Leavitt 1999;Messner et al 2013). An increase D r a f t in DOC in alpine systems could give smaller, UV-sensitive taxa a competitive advantage over endemic alpine species (Weidman et al 2014). Under these circumstances, the effects of warming may also add to these shifts, further supporting a community dominated by taxa of smaller size classes.…”