Effects of weather‐related episodic events in lakes: an analysis based on high‐frequency data

Abstract

2. We present data from high frequency monitoring stations from lakes in Europe, North America and Asia that illustrate two classes of abiotic effects of weather events: (i) generally short-lived effects of storms on lake thermal structure and (ii) the more prolonged effects of high rainfall events on dissolved organic matter levels and water clarity. We further relate these abiotic effects to changes in dissolved oxygen or in chlorophyll a levels.3. Three differing causes for weather-related decreases in surface dissolved oxygen levels were observed: (i) entrainment of anoxic water from depth, (ii) reduction in primary productivity, and (iii) increased mineralisation of organic carbon delivered from the catchment.4. The duration of in-lake effects tended to be longer for events driven by weather conditions with a longer return period, that is, conditions which were relatively more severe and less frequent at a site. While the susceptibility of lakes to change was related in part to the severity of the meteorological drivers, the impacts also depended on site-specific factors in some cases.5. The availability of high frequency data at these sites provided insight into the capacity of the lakes to absorb current and future pressures. Several of the changes we observed, including increases in carbon availability, decreases in PAR and increased disturbance, have the capacity to shift lakes towards an increased degree of heterotrophy. The magnitude and direction of any such change will, however, also 3 depend on the magnitude and direction of climate change for a given location, and on lake and catchment characteristics.4

Intra- and inter-annual variability in metabolism in an oligotrophic lake

“…We identified the thresholds for storm events as the days that fell above the 95th percentile of the precipitation (n = 938 days) or wind (n = 869 days) distributions, following Jennings et al (2012). The threshold for the classification of a storm was 19.5 mm of rain for a precipitation event and 11.2 m s -1 wind speed for a wind event.…”

“…For example, at the daily scale, photosynthetically-active radiation (PAR) is one of the primary controls on GPP and NEP, as phytoplankton respond to the diel cycle of fluctuating PAR over 24 h (Hanson et al 2006;Langman et al 2010;Silsbe et al 2015), whereas temperature is a primary control on R (Yvon-Durocher et al 2012). Seasonal variability in metabolism could be driven by changes in temperature or light (Hanson et al 2006;Langman et al 2010;Laas et al 2012), plankton abundance and succession (e.g., phytoplankton blooms, the zooplankton clear water phase), as well as by storms (Jennings et al 2012;Klug et al 2012;Staehr et al 2012). For example, Klug et al (2012) detected a decoupling of GPP and R in seven lakes in northeastern North America during and after Hurricane Irene in 2011, likely due to increased physical mixing and nutrient and organic matter entering the lakes from their catchments.…”

Environmental Impacts—Lake Ecosystems

“…Episodic events of extreme wind speed or rain events exceeding two standard deviations of the seasonal means have strong but complex impacts on thermal structure and stability, DOC loading and underwater PAR (photosynthetically active radiation) levels in northern European lakesthe magnitude and direction of change depending on the location of the lake and catchment characteristics (Jennings et al 2012). A comprehensive summary as to how extreme weather events affect freshwater ecosystems is provided by the British Ecological Society (BES 2013).…”

Networked lake science: how the Global Lake Ecological Observatory Network (GLEON) works to understand, predict, and communicate lake ecosystem response to global change

“…In particular, directional change is often punctuated or altered completely by events such as floods, droughts, heat waves, and severe storms, which are expected to increase in frequency and severity (IPCC 2014). Such events can lead to large changes in lake water quality and environmental function (Jennings et al 2012, Klug et al 2012) and can accentuate complex internal feedbacks among lake food webs and biogeochemical processes with surprising outcomes, such as toxic algal blooms (Qin et al 2010), which are on the rise worldwide (e.g., Carey 2011, Cottingham et al 2015) and pose an increasingly serious threat to humans and animals (Dodds et al 2009). …”