Potential anthropogenic regime shifts in three freshwater lakes in Tropical East Asia

Abstract

Regime shifts in ecology are characterised by major, often abrupt changes in ecosystem structure and functioning in response to one or more driving variables, or pressures. Changes in the provision of ecosystem services are a potential outcome. Despite the current combination of rapidly increasing pressures on what are often highly important socio‐ecological systems, the resilience of lakes in the warm tropics to human perturbation is far less well understood than those at higher latitudes. This paper focuses on evidence of aquatic ecosystem change from a cluster of three deep, freshwater, volcanic crater lakes (Yambo, Mohicap, and Sampaloc) at low altitude on the island of Luzon, Philippines. The lakes support different intensities of aquaculture, an important livelihood but also a driver of poor water quality throughout tropical Asia. Measured and monitored climate and water quality data, in addition to sedimentary evidence from sediment cores collected from the three study lakes, were used to determine the magnitude and trajectory of changes in lake water quality. Sediment cores were radiometrically dated and analysed for organic matter, spheroidal carbonaceous particles, and diatom remains. Diatom data were zoned numerically using cluster analysis. Diatom remains were also used to infer past variations in pH and possible relationships between potential driving climatic variables (temperature and rainfall). Diatom data sets were explored using detrended component analysis and principle component analysis. Despite differences in intensity of aquaculture, a common trajectory and timing of a potential regime shift, characterised by a replacement of benthic with planktonic diatoms and an increase in diatom accumulation rates from the early to mid‐1980s, is evident, and attests a low threshold for disturbance effects. A predominantly planktonic diatom flora has persisted even after recent improvements in environmental quality. The potential new regime may be less resilient and more susceptible to harmful algal blooms, abrupt expansions of anoxic conditions, and periodic mass fish kills when compared with its former state. The research further highlights the sensitivity of freshwater ecosystems in the warm tropics to disturbance pressures, and the risks to livelihoods, ecosystem services, and sustainable development.

A century of anthropogenic environmental change in tropical Asia: Multi-proxy palaeolimnological evidence from Singapore’s Central Catchment

“…This coincides with positive mean annual surface air temperature anomalies for Singapore since AD 1985, and is in line with recent warming-related increases in the occurrences of small centric Discostella taxa in lakes located in the Northern Hemisphere (e.g. Rühland and Smol, 2005;Wiltse et al, 2016;Yan et al, 2018) and in a cluster of deep, low-altitude crater lakes in tropical East Asia (Bannister et al, 2019). Nevertheless, given that climate-induced increases in water temperature tend to produce symptoms identical to those created by anthropogenic nutrient enrichment (e.g.…”

“…While there is a relatively large body of literature examining the impact of human activities on water bodies at temperate and polar latitudes (Jones et al, 2014; Rühland et al, 2015), effects on the functioning of freshwater ecosystems in the tropics remain poorly understood (Bannister et al, 2019). Freshwater ecosystems in the warm tropics, in particular, are characteristically different from their cooler climate equivalents.…”

Reply to formal comment on Griffiths et al. (2017) submitted by Gajewski (2020)

“…Temperatures, especially at levels that one might encounter in Arctic systems, have not been found to be drivers of dissolution. There is extensive literature from temperate and tropical lakes/ponds–diatom profiles recorded in lakes with water temperatures consistently over 25°C (e.g., [ 55 ]), illustrating that elevated temperatures are not in themselves a cause of dissolution. This should be evident to Gajewski, who co-authored a biogeographical study of Arctic diatom assemblages spanning a large temperature gradient from the Boothia Peninsula to northern Ellesmere Island [ 56 ] where it was concluded that “ Diatom concentrations (Conc) are not highly correlated with any measured environmental variable ” including latitude [ 56 ].…”

Philippine Seven Tropical Maar Lakes are Ideal Habitats for the Invasive Arctodiaptomus dorsalis Marsh, 1907 (Copepoda: Calanoida)

“…In most parts of the country, cases of unregulated aquaculture practices are pretty common, especially in some of the lakes in the province of Laguna (Mendoza et al 2019). Laguna is home to seven neighboring lakes, known as the SML, which are used for both aquaculture and tourism (Brillo 2016a, b;Mendoza et al 2019). Various studies have shown the declining water quality of the lakes brought about by increased nutrient inputs through excess fish feeds and domestic runoffs (Brillo 2015(Brillo , 2016aBannister et al 2019;Mendoza et al 2019;Mendoza-Pascual et al 2021), transforming it into an environment ideal for the propagation of A. dorsalis.…”

“…Laguna is home to seven neighboring lakes, known as the SML, which are used for both aquaculture and tourism (Brillo 2016a, b;Mendoza et al 2019). Various studies have shown the declining water quality of the lakes brought about by increased nutrient inputs through excess fish feeds and domestic runoffs (Brillo 2015(Brillo , 2016aBannister et al 2019;Mendoza et al 2019;Mendoza-Pascual et al 2021), transforming it into an environment ideal for the propagation of A. dorsalis. Papa et al (2012) reported that A. dorsalis was the only calanoid species in the SML.…”