On a razor’s edge : Maintaining lake ecosystem services and functions in an extreme world

Abstract

General introduction11 climate-based pressures are capable of hampering lake functions, and subsequently thwarting the possibility of reaching the established WFD goal, has become a pertinent question. This is particularly of interest for regions such as Europe wherein many lakes have been exposed to sources of continuous degradation, such as extensive urbanization. Abiotic repercussions of extreme eventsChanges to lake chemical processes as a consequence of climatic pressures have the potential to instigate significant ecosystem disruptions (Calderó-Pascual et al., 2020). Between extreme precipitation and warming events there can be ramifications on, for example, lake nutrient loading, water coloring, turbidity and water temperature. The increased runoff from extreme precipitation (Jennings et al., 2012) can affect surface water systems in a number of ways and is hypothesized to vary with the amount of anthropogenic land use in the watershed (Stockwell et al., 2020). Nutrient influxes can occur due to the runoff-instigated soil mobilization within the catchment, leading to large, diffuse depositions into receiving water systems (Ockenden et al., 2016). For example, a single extreme precipitation event can account for a significant portion of the total annual nutrient loading (Zwart et al., 2017). Nutrient pulses can boost phytoplankton growth on a short-term temporal scale, especially in oligotrophic systems (Carrillo et al., 2017;Morabito et al., 2018). Runoff into a system can also cause brownification (Feuchtmayr et al., 2019), which can lead to a decrease in light availability and an increase in water temperature (Weyhenmeyer et al., 2004). Similarly, the turbidity of a system could be altered due to runoff, stimulating the re-suspension of in situ sediments (Kasprzak et al., 2017). In turn, this can instigate decreases in water transparency (Kasprzak et al., 2017) and in light availability (Stockwell et al., 2020). Contingent on the hydrological and catchment composition, extreme precipitation will also impact the lake residence time of water and thereby nutrients and phytoplankton in a water system. A large influx of water into the system, for instance, can dilute the concentrations of nutrients within the lake (Cobbaert et al., 2014). Further, surface water bodies with outlets can experience a flushing effect with outflowing waters carrying nutrients from the system (Ho & Michalak, 2020). In such cases, an extreme precipitation event could assist with improvement of the overall water quality.Warming, such as through heatwaves, can influence chemical processes through different routes. These events can have a direct and noticeable impact on water temperature, which in turn can strengthen stratification within the water columns (Chen et al., 2019). Nutrients stored in sediments can also become bioavailable at higher water temperatures. This can occur when a stabilized water column promotes the release of nutrients from the substrate, which can then be redistributed in the lake from subsequent mixing of the ...