Hydrological regulation drives regime shifts: evidence from paleolimnology and ecosystem modeling of a large shallow Chinese lake

Abstract

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10 years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe.

Water Level Fluctuation under the Impact of Lake Regulation and Ecological Implication in Huayang Lakes, China

“…Meanwhile, there has been a phenomenon of eutrophication in Huayang Lakes, which was in turbid state in the past two decades. Lake water level regulation may not be favorable for lake restoration to a clear state [23]. Therefore, water level regulations need to perform multifunctionally, to not only fulfill flood prevention and human use, but also to exert less pressure on ecosystem health, especially on the growth of aquatic plants.…”

Profound Changes in the Physical Environment of Lake Taihu From 25 Years of Long‐Term Observations: Implications for Algal Bloom Outbreaks and Aquatic Macrophyte Loss

“…Nutrient loading is one of the most common causes leading to aquatic macrophyte loss and ecosystem shifts from a clear state to a turbid state (Scheffer et al, 2001). However, the critical nutrient level that a lake can tolerate before switching to a turbid condition and exhibiting an ecosystem shift may be influenced by a range of factors, including two important factors of SDD and water level (Kong et al, 2017;Scheffer & Jeppesen, 2007). Many studies have indicated that water level fluctuations and changes in the underwater light availability drive the succession of aquatic macrophytes in lake ecosystems (Geest et al, 2005;Havens, 2003;Squires et al, 2002).…”

A blooming business : Identifying limits to Lake Taihu's nutrient input

“…The original version of PCLake is calibrated based on 43 lakes in Western Europe , however, there are many successful applications for different locations around the world (e.g. Fragoso et al, 2011;Nielsen et al, 2014;Mellios et al, 2015;Kong et al, 2016;Rolighed et al, 2016) and also theoretical applications showing its potential to model climate change effects . PCLake simulates an aquatic food web consisting of algae…”

“…Besides, the critical nutrient load depends on local environmental factors which are subject to changes. For example, in case of wet years the critical nutrient load may be lower (Kong et al, 2016). Finally, in particular large lakes may be spatially heterogeneous and may therefore have a range of critical nutrient loads for different parts of the lake.…”

“…Due to human activities, these means of nutrient dispersal within ecosystems now increasingly differ from the past. Dust distribution alters due to climate change (Tegen et al, 2004), water flow is modified for instance due to the construction of dams (Kong et al, 2016) and megafauna have nearly gone extinct Doughty et al, 2016).…”